The four basic accessory circuits which were described in Part 4 of this Series can be adapted to cover most requirements on a GoldWing, so there is little need for more examples of what would be relatively minor variations on these themes.   So this further Article is about integrating accessory circuits when the opportunity arises, to avoid unnecessary duplication when several circuits are being installed.  Likewise to minimise clutter.

It’s also a collection of examples of how I or other people have tackled particular jobs, to illustrate the things that need to be taken into account and that sometimes there is more than one perfectly valid way of going about things.

Lots of accessory circuits inevitably means lots of cables and connections, so that prime locations like under the seat and under the glove boxes can get very busy and crowded.  The first photo shows the numerous cables, connectors and (white tape) labels under my right hand glovebox or, since it’s an airbag model, non-glovebox because it’s just a space with a lid on it, quite a lot of which is already taken up with components.

There are service connections in here, notably of cables routed to this space from the handlebars (eg switch cables) en route to the space under the seat.  Other cables bring accessory power supplies from under the seat for two different display lighting circuits, so that groups of LED lighting units can be connected to them.  Finally another multicore cable terminates here, routed from under the seat, installed while the Top Shelter was off to provide spare capacity.

Each cable in this space, or at least each separate bundle of cables, is labelled with its role using a tag of white pvc insulation tape tape and a marker pen, as an aid to identification.  So things in that space are not as chaotic as first glance might suggest.  You will see from the second picture that everything can all be tucked away neatly before the lid goes back on.  Unless you are systematic about what you do and also pretty diligent about recording and labelling things as you go along, it can easily become difficult or even impossible to sort out what’s what.

Let’s start this collection of ideas and tips, for that’s effectively what is is, by explaining how it can help to share cables between circuits, especially around groups of relays.

A Common Ground Connection Loom

One easy way to apply a bit of joined up thinking to your accessory circuits is making up a Common Ground Connection Loom under the seat.

For technical reasons (which I don’t understand but seem to make practical sense by somehow reducing audio interference ) it is undesirable anyway to make the return connections from accessory circuits directly to the battery’s negative terminal.  And if you did try to connect all the return cables from your accessory circuits to the battery’s negative terminal you’re going to end up with a jumble of cables and ring terminals; even if you don’t run out of space to make enough connections your bike’s battery will look very cluttered.  Installing a Common Ground Connection Loom solves this problem and leaves your battery uncluttered and therefore much easier to remove if you need to.

“Ground”, in the context of motorcycle electrics, means the bike’s metal frame and the engine block, which are always very well connected, electrically speaking, with the negative terminal of the battery.  Honda installs a heavy duty cable connection between the battery’s negative terminal and the engine/frame, not least because the engine block carries the return current when the starter motor is working.  Honda also connects ground returns of the bike’s circuits (headlamps, horn etc) to this or other frame connections.  So the  engine block and frame are, electrically speaking, the equivalent of the battery’s negative terminal for purposes of returning accessory circuits too.

It is therefore possible (although not usually desirable) to connect the second terminal of almost any accessory to any nearby part of the engine or frame.  For example fog lights, which are installed low down and in front of the engine, can have their return connection made to one of the bolts on the engine nearby.  But it’s not really a good idea to do this and generally speaking Honda doesn’t do it all, preferring instead to run a return cable back thought the wiring loom to a central grounding point.

The main reason for this is reliability.  Multiple grounding connections all over the bike’s engine and frame is a recipe for multiple poor earthing problems – and poor earthing problems can be a nuisance to diagnose and fix.  Better therefore that your accessory circuits have reliable connections to ground.

Grounding connection points elsewhere on the frame may be in exposed positions and so prone to corrosion; the engine or frame bolts you fancy using may be doing a critically important job of their own and really shouldn’t be disturbed – or the engine or frame bolt which you choose might provide a relatively poor electrical connection anyway because of non-conducting gaskets or bushes built into the attachment.

Better therefore, generally speaking, to copy Honda’s approach to circuit design by using return cable from accessories back to a central, reliable grounding connection point.  And since the cable runs for many of your accessory circuits are likely to start off under the seat, where there is space to install connectors and relays, the obvious place to establish your common grounding connection point is under the seat too.  Fortunately on a GL1800 the attachment bolts which fasten the rear sub frame (which supports the trunk and saddlebags) to the main frame are under the seat and they provide a convenient and reliable place to connect to ground.

The first photograph in this Section shows a black 35 amp cable connected (as a common grounding point) by means of a yellow crimp terminal with an 8 mm ring to the right rear frame bolt of a GL1800 under the seat.  The grounding cable is then routed forwards under the seat to the area between the relay box and the fuel tank sender, where Honda has kindly left space suitable for installing accessory relays and making circuit connections.

This common grounding cable can then provide a return connection point for all the bike’s accessory circuits and for your relay energising circuits.  The cable must of course be able to carry the full current load of all the accessory circuits using it simultaneously so it needs to be quite a thick one.  Likewise each branch of this cable needs to be able to carry the full load of all the circuits connected to it.

In practice you will know (by the number and size of fuses you have incorporated into your accessory circuits roughly how much they will draw in total, which will provide a useful starting point.  Unless you have an exceptionally large number of power-hungry accessories, a cable rated at 30 amps or above is likely to be more than sufficient.  If you haven’t got any 30 amp cable you could use equivalent multiples of thinner cable, say two 16.5 amp cables or three 11 amp cables.  If in doubt overdo it!

At its other end, in the area under the seat where you will be making your accessory circuit connections, you can use thinner cables and butt crimp connectors to branch out so that returning accessory circuits can be grounded by connecting to it.   You can also use it for other connections you will need to make to ground, such as the returns from relay activation circuits.

Sharing Power Feeds to Relays

A similar approach, branching a thick cable into thinner ones, can be used to connect the 12 volt power supply to each Terminal 30 (power input) of a group of relays or directly (i.e without relays, although via fuses of course) to accessory circuits.

On my own bike I have installed a row of four relays, taped together for tidiness and labelling, under the seat.  An in-line fuse (rated at 30 amps) is connected to the battery’s positive terminal and then to a heavy cable (over 30 amps) which connects in “daisy chain” fashion to the Terminal 30 (power input) of each relay in turn.  You will need to use large (yellow) female push-on crimp terminals to make up this type of daisy chain.  It may be necessary to trim out a few strands of cable and to chamfer the insulation as two cables come together to enter the crimp tube in order to get them in but with care it can be done.

Start by taping the relays together, to give your self a stable set of blades to work with, having oriented them so that they all face the same way.  Then measure how much cable you will need for each cut the loops and cut them to exactly the same length before you start; this will give you a neater final result.

Branching power outlet cables from relays

Sometimes one relay can serve several circuits.  For example on my bike Relay Number One  (which like them all has a full 30 amp input to its Terminal 30) and is energised by the Accessory Terminals (so its output Terminal 87  goes live when the ignition is on, branches into four fuse-holders which connect to four different sub-circuits.  It doesn’t matter than some (the low power ones) are switched and some aren’t, or that they vary considerably in the potential current draw because they are individually fused to suit.

Each relay’s Terminal 87 (power output) is connected to the circuit’s (or circuits’) own in-line fuse(s), rated for the appropriate load and hence cable size.  These sub-circuits can also be branched out into subdivisions too if necessary, as long as they are all fused to suit their load and cable size.  So one relay can cater for a large number of sub circuits, far more than I have used.

Relay No	Role	Operated By	Load	Sub-Circuits
1	Accessories	Acc Terminals	15	Heated Clothing (10) Amber Lights (2) Spare (5) Spare (5)
2	Blue Display	Switch	7.5	Three, each 2 amps
3	Red Display	Switch	7.5	Three, each 2 amps
4	Strobe lights	Switch	15	None
5	Fog Lights	Switch	10	None

These are of course merely examples, chosen to suit my particular range of accessories.  My bike is a US Specification GL1800, so a fog light circuit was built into the bike’s wiring loom by Honda, but I’ve included a fictitious fifth relay, which I would have installed for a fog light circuit it was a UK Spec bike.  Power circuits which need to be switched separately, such as  fog lights, need their own relay.

Note that Relay Number 1 is energised by the bike’s Accessory Terminals rather by an operating switch, which means that its sub-circuits go live as soon as the ignition is on.  The cable connected to the power output terminal of this relay therefore branches immediately into four in-line fuse holders for the four sub-circuits, each of has a fuse rated according to that circuit’s load (and of course it’s cable size).

Shared Grounding of the relay energising circuits

A similar “daisy chain” approach can be taken with the cables connecting Terminal 85 of each relay, the ground return of the energising circuits, which can then be connected to the Common Ground Loom which you have also created.

Note that because relay energising circuits draw only tiny currents (less that 0.2 amps each) you can use thin cable for this daisy chain because (assuming 5 relays) the total current on all four will not exceed 1 amp.  You can therefore safely connect this daisy chain of Terminal 85 cables to a thin cable branch of your Common Ground Loom.

Sub-circuits and fuses for your Display Lighting Circuits

While some accessories, such as fog lights and powerful strobe lights need their own accessory circuit and relay, display lighting units, which are usually low power devices, can profitably be grouped together.  Of course if your display lighting includes something really powerful and spectacular it might warrant its own relay circuit (or in the case of PapaJoe’s Blackpool Tower Trailer it’s own mobile Power Station!) but for individual LED lights and LED light strips and arrays, grouping together makes excellent sense.

Because the cable supplied with LED lights is usually very thin, the circuit to which it is connected needs to be fused accordingly.  So your shouldn’t, for example,  group lots of LED lights and other lights and then fuse the whole lot with one 7.5. amp fuse.  If a short occurs in the thin power lead of one of your LED strips it would burn up before your 7.5 amp fuse blows.

Even fairly long strips of LED display lighting draw a relatively low current, so you can illuminate a sizeable chunk of a GoldWing with a current draw of 2 amps or less.

I decided to establish three connection “hubs” for each of two colours of display lights for display lights on my bike, one under each glovebox and one under the rear of the seat.  These locations would be reachable by the power leads supplied with the LED strips and lights from the positions on the bike where I was planning to install them, so three “hubs” would be enough.  Since I wanted to be able to switch between two colour schemes of display lights I would need one set of three hubs for each colour.

It can be difficult to calculate the precise current draw of a group of LED strips without resorting to actually measuring it, which I decided would be possible but fiddly and was probably unnecessary.  LED lights draw tiny amounts of electricity and even a long strip of LED lights is unlikely to draw more than 1 amp.  Instead I decided to fuse the power cable of each “hub” at 2 amps (the lowest size of blade fuse available) on the basis that a short of 2 amps, even in a thin LED strip power cable, would not be a serious fire risk.

If I find that as I add more LED lights to a hub its 2 amp fuse blows, I will have to consider establishing sub-circuits downstream of the hub and fusing those at 2 amps.  If all the sub-circuits are separately fused, which they should be because it should be all or none, the hub’s fuse (back under the seat) could be increased substantially, indeed to as much as the cable supplying power to the hub is rated to carry.   (It would not be unreasonable to try increasing the hub’s fuse to 3 amps before resorting to creating fused sub-circuits downstream to see if that solves the problem.  But it would not be safe to increase the hub’s fuse much higher than that without creating sub-circuits and certainly not to match the capacity of its cable.)

Branching Relay Power Output Cables

Providing there is no requirement for separate operating switches (or providing the sub-circuits you will be creating can be switched at their full power levels) you can branch the power output from a relay.  Providing the cable feeding power to a relay can handle the total current you will draw from it, you can branch its output up to the capacity of the relay if necessary, which will be 30 if not 40 amps.  Relays are specifically designed to switch high current loads.

For example on my bike the relay power output connection (Terminal 87) for each of my two display colours has a main circuit fuse (in this case 7.5. amps) and then the cable branches into three, each of which has a further  in-line fuse (the individual hub fuses) rated at 2 amps.   I then use twin core (red/black) automotive cable to feed power from these sub-circuit fuses to “hubs”.

The black cores of these hub-feeder cables are connected at their origins under the seat to the Common Ground Loom. Two colours, three hubs each, so on my bike there are six hubs in total, so six return cables to be connected to ground.  You will begin to understand how cluttered the battery’s negative terminal would be getting by now if a Common Ground Loom wasn’t being used!

Power distribution “hubs”

At the other end of each of these three twin core red/black feeder cables are branched to provide for multiple connections.  Both red and black cores are branched equally and sufficiently to allow for some spare capacity.  As LED lights and strips are added to the bike, their power leads can then be connected, in groups when the opportunity arises,  to one or other of the branches, positive to red, negative to black.

The branching “hub” pictured here was constructed by squeezing as many cables as would go into the crimp tubes.  The total number of branches created turned out to be seven (so seven reds and seven blacks) each of which terminated in a red-size crimp tube with an open end, ready to accept an LED power lead.  Because the end of each branch is an insulated crimp tube it is safe to be left open until it’s needed.

Bearing in mind that on my bike each hub location has two of these “hubs”, one for each display colour, and that each red-size crimp tube will take several LED power leads (because their cable is so thin) you are pretty unlikely to need seven branches.  Except perhaps for the hub under the seat, where there is more space available so less of a need to avoid overkill, a smaller number of branches will almost certainly suffice.

Crimping in confined spaces like under the glove boxes can be awkward and although you don’t want to end up with too  much cable to be able to tuck away, you need to allow for lifting your “hub” out of its hole sufficiently to crimp the joints when it’s time to make them.

For this reason it makes good practical sense to construct the branching hub end of the feeder cable on the bench before installation and to route the un-branched end towards the area under the seat rather than the other way around, for example by drawing the plain end backwards from the glovebox under the Top Shelter rather than the branched end forwards.  More about how to do that without taking the Top Shelter off in a later Article.

LEDs are polarity sensitive

LED lights and strips will only work if they are corrected the right way around.  LEDs are light emitting diodes and diodes are devices which will only conduct electricity in one direction.

Connecting a packaged LED lighting unit (eg a strip or a set of LEDs) which is designed to work at 12 volts the wrong way around (i.e. the positive to negative and vice versa) will not normally damage it, it just won’t work that way around.  Testing for the correct way to make the connection is therefore simply a matter of trial and error – but check the instructions which come with it before you do so, in case the set you’ve bought is unusually sensitive.

Note however that this is not normally true for single LEDs, indeed usually it isn’t – but they’re not usually designed to cope with a forward voltage of 12 volts per LED either and a resistor has to be used in series with it to drop the voltage.  Installing individual LEDs, either singly or in combination, calls for enough skill to calculate the size of resistor to use to ensure the correct forward voltage is applied to each LED.

The power leads of LED lighting units are sometimes, but not always, marked positive and negative in some way but doubt can arise.  If in doubt make a temporary test connection (for example to a spare 12 volt battery on the bench) before crimping up connections on the bike.  If an LED light unit has a power cable which is unmarked or ambiguous, I test before installation and mark the positive cables by tying a knot in them.

Sub-Circuits from the Accessory Socket(s)

The GL1800′s Accessory Socket is under the left glovebox inside a rubber hood and it can be difficult to get to.  On early GL1800s (or at least on US models) there is also an Accessory Socket under the right glovebox too.

The Accessory Socket provides a useful source of power for low power devices which are likely to be installed nearby such as an MP3 player which can live in the glovebox and also make use of the auxiliary audio connector which is under there too.  Other accessories which have their own operating switches like satnav and speed camera detectors/warning devices, which are likely to be installed on the handlebars or the dash.

The accessory Socket is a three way Hitachi-type socket, although only two contacts are installed in it.  Not least because the Socket is buried too deeply inside it’s rubber boot to allow to the cut it off and replace it with standard connectors, to connect anything to it you will need a three way Hitachi plug and two 2.8mm crimp blade terminals.  These are available as kits of plug housing plus three blades from Kojaycat Ltd.

If you are planning to connect more than one device to the Accessory Socket you will need to branch the cables from your Hitachi plug.  It is fiddly and unreliable to branch cables directly from a 2.8mm blade crimp terminal so better to attach a short length of cable to the plug and branch from there.  You can do the branching using standard butt crimp joints instead of more Hitachi connectors.

Bear in mind that the Accessory Socket is protected by the bike’s 5 amp Accessory Fuse and the total permissible load on the Accessory Terminals and Accessory Socket(s) combined is only 5 amps – so this is no place to be trying to draw power for heated gloves for example.  Each branch you create at the Accessory Socket will form a sub-circuit and should therefore have its own fuse, especially if the devices to be powered from it consume only a very small current (less than 1 amp) in which case they are likely to have pretty thin power leads.  Glass tube fuses may be better suited to this role than blade fuses, since they are available in ratings below 2 amps. Using 2 amp blade fuses wouldn’t be unreasonable either.

Advantages of Bullet Connectors for “Hubs”

Butt crimp connectors are not expensive and so replacing them as a way of re-making a joint isn’t a big deal providing you have left a little bit of spare cable length.  But a pair of bullet crimp connectors (one make, one female) provide an attractive alternative because they can be disconnected and re-connected at will and without tools, so they also constitute a service connection.  They take up a bit a tiny bit more space than a butt connector, they are less secure in that they can be pulled apart and using a pair of bullet terminals costs more than one butt connector.  And because any male bullet (of the same colour) will fit any female bullet, they are not as foolproof for purposes of service connections when there are multiple circuits passing through, but nevertheless I find them very useful and now routinely use them for display lighting hubs, primarily because they allow the various branches of a hub to be disconnected in turn to aid fault-finding if the hub fuse does blow.

In order to be able to leave spare hub branches unconnected safely (and to help avoid mistakes when reconnecting) it’s important to use female bullet connectors for the upstream (i.e. potentially “live”) 12 volt positive supply cables and male bullet terminals for the (lifeless) circuit return cables.  It doesn’t mater if a circuit return cable end contacts the bike’s frame or another return cable, so it doesn’t have to be insulated before the ends are tucked  away.

a black (return, ground) hub cable can touch anything when it’s tucked away. (The power leads for your LED lights therefore have male bullets on the positive cables and females on the negative ones, so they connect the right way around.)

A weighty investment

Service Manual and Wiring Diagrams

Interfering with your bike’s wiring loom in any way without access to (and being able to understand) your bike’s wiring diagram is like flying blind; you really shouldn’t do it.  Classic GoldWings has much simpler electrical systems than the later ones and Honda does use a consistent colour scheme for its wiring looms, so with older bikes it’s maybe not so critical.  But tinkering with the wiring loom of a GL1800 without a wiring diagram to refer to is asking for trouble and in the case of an Airbag Model it could get very exiting indeed.

Honda Service Manuals for current models can be purchased and these include wiring diagrams but it is important to understand that wiring diagrams can vary considerably between model years and for different markets.  So for example there have been several editions of the Service manual for a GL1800 since it’s first introduction and the wiring loom on a UK specification GL1800 is significantly different from that of a US specification bike of the same model year, especially the lighting circuits.  UK bikes have front “side” lights, US bikes don’t; US bikes are pre-wired fro fog lights, UK bikes aren’t; UK bikes have two tail lights, US bikes have four; US bikes have amber forward-facing running lights in the mirror housings which occult to indicate a turn, UK bikes have flashing amber direction indicators only.

The Honda Service Manuals you can buy in the States will not include wiring diagrams for UK specification bikes which can only be obtained through UK Honda Dealers.

Clymer and/or Haynes Manuals are available for GoldWings from 2005 and earlier and they include wiring diagrams but generally not those for UK specification bikes.  There is as yet no Clymer manual for 2006 onwards GL1800s.

Wiring diagrams for older model GoldWings are also problematic but (albeit currently under threat of being closed down by Honda’s lawyers) there is a useful Website called GoldWingDocs from which wiring diagrams cab be downloaded.  Kojaycat also supply their own wiring diagrams for some GoldWing models.

Altering your GoldWing’s Wiring Loom

Honda did a careful and diligent job designing your bike’s wiring system and the Cautionary Tale in Part 1 of this Series should be a warning to all DIY auto-electricians to think long and hard before interfering with the bike’s own circuits.

It’s possible to end up doing this inadvertently and even without making any connections to the wiring loom, for example simply by routing your accessory cables alongside elements of the existing wiring loom you can cause audio interference or worse.  The golden rule when you engage in DIY wiring on a GoldWing, especially the later models like the Airbag GL1800 which has an elaborate wiring system some of which really must be left alone, is to proceed step by step and with caution, testing as you go to make sure you haven’t compromised any of the bike’s functionality.

On my own bike I have, with due caution, made three modifications to the manufacturer’s wiring system so far and thankfully they do work and haven’t so far compromised anything else, so I will describe them as illustrations of what can be done.  But don’t try this at home unless you are sure you are doing it safely and correctly; I studied the bike’s wiring diagram in some detail and checked and re-checked what I was about to do before cutting into the wiring loom.  I also made sure that I could completely reverse what I was doing before I did it by connecting the bike’s wiring loom back the way it was.

Cutting into Headlight cables to install a Modulator

As part of my quest to be conspicuous (for my own safety, honestly Your Honour!) I have installed a headlight modulator on my bike.  This is a device which causes the bike’s main beam headlights to pulse on and off in turn, like ambulance and police car headlights do.  (Headlight modulators are legal in many countries on motorcycles as a safety aid, as are flashing lights on pedal bicycles in UK.  But modulators are not legal for road use by motorcycles in UK, so be warned.  Nor of course are strobe lights or any flashing lights at all except lights reflected in a rotating road wheel.  For purposes of this Article it’s the installation of this device rather than its use or legality which we’re covering.)

Headlight Modulators are available commercially in the US but mine was made for me by a friend who has electronic skills.  For purposes of installation it’s simply a black box with cables coming out of it, four of which were for incoming and outgoing connections to the headlamps’ power cables.  The box also has cables for an operating switch and for an LED indicators light, to show when the black box was active.   I had taken care to emphasise to my firend when I got him to make it that the black box must be “fail safe” in the event of any type of failure – so that the power connections to the headlamps would be on, as the manufacturer intended.  Effectively therefore the two pairs of in/out headlamp power cables are internally connected unless the black box actively interrupts them.

Our concern here is the way these two pairs of black box power cables are connected into the bike’s headlamp circuit, so I will mention only in passing that I chose a momentary press switch (i.e. a push button) to operate the device, so I could not be inadvertently left on.

The GL1800 has two main headlamps and two dipped beam headlamps.  If you’ve been followed on the road by a GL1800 you will know that the dipped beam lights don’t alway both show up; it depends on the angle of view.   I would therefore be installing my modulator on the main beam lamps rather than the dipped ones.

On studying the wiring diagram the safe option was to intercept the main beam headlamp cables close to the lamps.  This is because a GL1800′s main beam head lamps are (at least on my US Spec GL1800A8) supplied quite separately, one from the power output of a dedicated relay but the other one directly from that relay’s energising circuit.  The headlamp dipping switch also has a cable connection to the bike’s starter switch, so that when the starter motor is turning the headlamps are turned off temporarily.  One way and other it was going to be far simpler  and safer to interrupt the power supply to each headlamp close to the bulb holders.  And fortunately the main beam (outer pair) lamp units on a GL1800 are reasonably accessible from behind the dashboard.  So that’s where I chose to tackle them.

Having checked several times that I had identified the correct cable on each side, I cut them, bared the ends and connected lengths of suitably rated cable to each one, so four cables in total, which were then routed to the location where the black box was to be installed.   The headlamps are 55 watts each, so a nominal 4.5 amps each, so up to 6 amps at 14.3 volts, so I used 11 amp cable to allow plenty of spare capacity.

I also used different colours of cable to help avoid getting them mixed up; it was important to connect the bike’s two headlamp power source cables to the black box’s two input cables and then the black box’s output cables to the two headlamps.   To provide a service connection which would be reliable for purposes of connecting these cable in the correct permutation I used a four way multipin connector.  I installed a four way socket on bike’s side and plug on the black box side.

Using a multipin connector also allowed me, by making up a spare four way plug with short loops of cable which, when inserted instead of the black box plug, would restore the normal cable pathways to the headlamps.  This spare plug was attached to the cable run close to the connector using a cable tie, so it would always be handy, just in case.

The installation worked and there were no unforeseen consequences for the working of the headlamps or anything else on the bike.  It would have been challenging (because of awkward access) to re-connect the original headlamp cables precisely where I had cut them but replacing the black box with the spare plug would have the same effect.  The installation was therefore easily reversible.

Before undertaking this installation I took particular care to:

1. Study the bike’s wiring diagram to ensure I was cutting into the bike’s wiring in a safe place  (if I had cut into the headlamp cables near the headlamp relay under the seat it could have got very complicated).
2. Cut the3 cables in a place where I could if necessary (albeit by taking the fairing off to get access) rejoin the cut cables in precisely the original configuration
3. Make provision to restore normal connections anyway (by using the spare multipin plug) so even if my new gadget self-destructed completely I could easily restore normal function.
4. Do the job in a way which would allow the whole installation to be completely reversed almost without trace.

And these are perhaps the golden rules of what you should aim for if you decide to cut into the bike’s wiring loom in any way.

And the fifth rule, perhaps the most important of all, is that before you start you should weigh carefully whether what you are doing has sufficient value to be worth the interference with the wiring loom you are going to inflict.  I envisaged that my headlamp modulator would be valuable when I was filtering through traffic on motorways, to get the attention of the drivers  I was filtering past, so they would at least know I was coming and might even move over a little.  In practice I have almost never used them and if I was starting again I definitely wouldn’t bother.  (Strobe lights are much effective!)

Switching off Headlamps and Tail Lights

Another modification to my bike involves interrupting the power supply to the dipped headlights and tail lights with switches, so they can be turned off.  Only early UK model GL1800s were equipped with a lighting switch  by Honda so mine doesn’t have one.  Normally I would always ride with headlamps on anyway, for safety reasons but in order to use colour-themed display lighting, I wanted to be able to switch them off sometimes.

One option would be to use a changeover relay to switch each set of lights off, which would have been even safer because the switch position which kept these lights on would be “normally closed” and only when the relay was energised by the operating switch would the power circuit to the relevant set of lights be disconnected.  In this scenario if either the operating switch or the changeover relay failed the head and tail lights of the bike would work normally.

A changeover relay has five blade connectors rather than four, the fifth one being Terminal 87a which is “normally closed” in relation to Terminal 30.  Terminal 87 is “normally open” in relation to Terminal 30 and this pair are therefore used for power circuits as described in the previous Article in this Series.  Hence they are  called changeover relays because the connection from Terminal 30 will be changed from Terminal 87a to Terminal 87 whenever the relay is energised.  By connecting the power cable of the relevant lighting circuit into Terminal 30 and out of Terminal 87a the relay will disconnect the power when it’s energised.

But where in the wiring loom would it be safe and practicable to interrupt the headlamp and tail lamp circuits safely?  That was the question.

Isolating the Tail Lights was not as difficult as I anticipated.  The tail lamp circuit also powers other lights, for example the front “side” lights on UK models and on US models the riding lights in the mirror housings, which on my bike powered the rear-facing, red mirror edge LED lights, which I wanted to leave on for safety reasons.   Fortunately the wiring diagram (for my bike at least) shows a multipin connector located under the seat beyond which the power cable (and there’s only one for all tail lights at this point) is connected only to the bike’s red rear lighting and number plate light, all of which I wanted to be able to switch off.  This power supply is also used (downstream of this connector) for the red saddlebag and trunk trim lights, so they would also be extinguished at the same time, also what I wanted to happen.

From the wiring diagram and the component location list which the Honda Service Manual also lists, I was able to identify the colour, size and location of the relevant connector and the colour of the cable I needed to cut.  Even with these strong clues it was quite a search.  The relevant connector, not normally requiring access, was tucked well away out of sight. Without the help of the component location list in the Service Manual I would probably still be hunting for it.

Although it was not difficult to ease out of its protective rubber boot and disconnect, there was only one side of the connector with enough slack available to break into the loom and I had to cut back quite a long length of wrapping tape and open up some of the loom’s pvc sleeving to gain sufficient access to the cable I was aiming to interrupt.

Having found it and freed it for cutting, I checked and re-checked before cutting it far enough away from the connector to retain a tail long enough to connect to – and if necessary to cut again to reconnect to if I had got it wrong after all.  Before doing anything else I checked that the tail lights no longer worked.  So far so good; I had chosen the correct cable to cut.

I then bared the cut ends and attached different coloured cables to each one, to help distinguish upstream from downstream.  I chose 8 amp cable, my garage stock size, as sufficient, on the basis that my bike had four 5 watt tail lights plus a 5 watt number plate lights, so a total of 25 watts and therefore a total of 2.5 amps at most, plus the LED trunk and saddlebag trim lights and a trunk spoiler led light, so maybe another 1 amp.

Opposite combinations of male/female bullet crimp connectors were used to make these joints, so that the normal circuit could be restored simply by connecting the cut ends together again if necessary.  (A pair of bullet connectors will, if necessary, allow you to reconnect a cut cable even if you have inadvertently shortened it slightly.)  I also took care to use a female bullet connector on the power side of the cut, so even if it became disconnected there would be no risk of it shorting to the frame.

I then led the pair of “extension” cables forward under the seat to where further connections would be made to complete the job.  More of that later.

Headlamp Circuit interruption was more problematic and also involved careful study of the wiring diagram.  The dipped headlamps (unlike the main beams) are both supplied by a power circuit from a dedicated relay.  I therefore could choose whether to cut the energising supply to the relay or the power supply coming from it.

No contest here, the low current energising cable was the obvious one to interrupt; no point introducing another switch to a power circuit which was already being switched by a dedicated relay, much better to go for its controlling cable instead, even if I was going to use a changeover relay to do the switching.

So I checked and rechecked the wiring diagram, freed up the relay box under the seat and exposed the wiring loom serving it, identified the dipped headlamp relay and then (by colour coding) the energising cable leading to it.  And then I cut the cable, tested that the headlamps no longer worked, then bared the ends and attached different coloured extension cables, as with the tail tight interruption.  Since I was interrupting the energising circuit rather than the power circuit the current involved would be less than 1 amp but to be on the ultra-safe side I used 11 amp cable, as with the tail light supply interruption.

Changeover relay or direct switching, which was it to be? Bearing in mind that the current draw on the headlight circuit I was interrupting was less than 1 amp and the tail light circuit was no more than 3.5 amps, these currents were both within the safe capacity of the handlebar accessory lights I was thinking of using.  Was it really necessary to incorporate changeover relays?

And was it necessary to use handlebar mounted switches anyway?  These light would normally be left on, so why no use a switch located somewhere else, perhaps somewhere in a more sheltered location?

I thought long and hard about whether I could trust a handlebar accessory switches with my bike’s essential riding lights but eventually I decided that switches on the handlebars, where I could see them and use them easily and so check their functionality easily and see at a glance whether the switches were in the “on” position would be best.  I was also satisfied, since the biggest current involved was 3.5 amps, I could dispense with the idea of using changeover relays in favour of direct switching.

However the standard handlebar accessory switch set, designed to distribute power from a single input cable to three output cables, one for each switch, so a total of four cable, could not be used for this purpose.  I therefore modified my switch set internally so that each switch has its own pair of cables, so six cables in total, with no internal bridging at all.  All six cables had been routed, via service connections under the glovebox, to the space under the seat.  All cables were rated for at least 5 amps.

I was therefore able to select two of these switches and to connect the extended headlamp and tail lamp interrupt cables for headlamps and tail lamps to them, again using opposing male/female bullet connectors to facilitation restoration of uninterrupted headlamp and tail lamp circuits at these connections under the seat if either switch failed open.

Next Article

The next Article in this Series will cover the routing and protection of cables and the location of display lighting units.

Installing display lighting and associated power leads inconspicuously so that the bike looks impressively lit in darkness but still looks like a bike in daylight (and not like it’s had a box full of stick on toys and fridge magnets thrown at it) calls for a combination of artistic flair and attention to considerable detail, especially when it come to hiding the power leads.  Routing cables from handlebars switches around the steering head also calls for care to avoid cables being stretched or nipped.  Thin-walled automotive cables and the very thin power leads of LED lighting units also frequently calls for careful securing and protection using sleeving and/or cable ties.