Advice for Installing Electrical Accessories on Motorcycles

How to add lights, ignition mods, or other electrical accessories to your motorcycle without frying your wiring. By Mark Zimmerman.

Installing electric gadgetry is a time-honored motorcycling tradition. The big difference between, pardon the pun, current models and the bikes around when I commenced stitching wiring harnesses together is that modern motorcycles' electrical systems generally don't fry themselves into a gooey mess the first time you power up your new driving lights. At least they don't if the lights are properly installed.

Obviously, the job must be done in a neat, workmanlike and professional manner. If it isn't, you're only asking for trouble, and it's the sort of trouble that generally results in a barbecued wiring harness, a cooked motorcycle and a possibly well-done rider, usually at 2 a.m. on a deserted road. The odd thing is that while most of us pay fairly close attention to installing things like brake calipers, exhaust systems and saddlebags, the same guy who'll torque the bolts, apply thread-locking compound and double-check all the lock tabs on his new brake rotor will install an electrical accessory with a household-wire nut and two yards of friction tape. Makes you wonder, doesn't it?

Really, It's Not that Hard

Aanyone with a modicum of horse sense and a few commonly available hand tools can create a proper connection. Put a few connections together and baddabing, as they say in the big city, you've got your electrical project completed. Rather than cover old ground, I'd suggest reviewing the previous article should you have questions regarding basic electrical procedures.

There are three basic wiring scenarios. First, the direct replacement plug and play situation, wherein a stock component is replaced by a new one, for example installing a new FI or ignition module. The second example is where something like a taillight modulator or additional lights are plugged or spliced into an existing circuit. Chances are some crimping or soldering skills will be required here. A third alternative might be adding a separate circuit altogether, for instance a power take-off point or an accessory plug, but since these are usually plumbed directly to the battery, and many new bikes come with a prewired power outlet, I'm going to lump them into the add-on category.

Before we start soldering, crimping and installing, let's cover a few preliminaries so we don't end up cussing, sweating and ruining. First, take the time to thoroughly read and understand the manufacturer's instructions. This is particularly true if you're planning on installing two accessories at once. A perfect illustration would be the rear running lights and flashing brake-light module we've installed in the accompanying photos. When the lights are installed separately they're wired one way. However, when the optional flashing brake-light module is added into the circuit, the wiring must be modified slightly.

Like any good scout, come prepared. At the least you'll need a few basic hand tools, including crimping pliers, some high-quality electrical tape and a few extra tie-wraps. Of course, some dielectric silicone grease won't hurt, and a test light may also prove handy. Normally, I'd expect to find all the necessary connectors included with my new gadget, but stuff happens, so it might be wise to have a few electrical connectors on hand just in case the dog eats one or something. If heat-shrink tubing insulates the connections or protects the wiring, you'll need a heat gun or a hot-air hairdryer. Although it's not a strict necessity, it's always handy to have a shop or an owner's manual handy, particularly if you aren't familiar with the preliminary steps that may be required, such as removing the side panels or fuel tank.

It Took Me Forever to Learn this Stuff

Wiring up accessories is a straightforward job, provided you follow the manufacturer's instructions. Without belaboring the point, paying attention to the directions normally eliminates 99 and 910ths of the problems associated with electrical installations. But the manufacturer may assume you've done this before, which is never a safe assumption, and there are always some situations that arise due to peculiar circumstances. Since I'm pretty familiar with both peculiar and run-of-the-mill, here are a few tips to make things easier.

Occasionally, you may need to extend the attached wiring or supply your own wire to connect the component to your bike. If the supplied wire is just a bit short, the obvious thing to do is match what you need against what's already there. But what if they don't carry that particular size down at Harry's wire emporium? The rule of thumb is to use the next-larger wire size. And if you have no clue as to what wire size you need? No problem. First, add up the amperage, or watts, in the circuit. You'll need to contact the manufacturer if this info isn't provided with the accessory. Next, measure the length of wire needed, including the length of the ground wire, if any. Once you know how much current will flow over the required length, you can select the appropriate wire gauge from any wire manufacturer's catalog.

Wire isn't particularly expensive, so don't scrimp. It's better to have an extra inch or two than it is to have the wires pulled taut. A tight wire is more likely to pull off its terminal or wear through its insulation as it bends around the frame. Give some thought to the wires' routing. The most direct route may not be the best, especially if it forces the wire into a tight bend or drags it across a sharp-edged weld or anything else that's likely to abrade through the insulation and cause a problem. It goes without saying that wires should be routed as far as possible from hot engine parts. Whenever possible, route any new wiring through the bike's factory wiring harness, or at least along the side of it. And don't just let it dangle there. Use tie-wraps to hold it to the frame or existing harness. If you really want it to look professional, run exposed wiring through plastic or fabric wiring loom, available at any auto-parts supplier and many motorcycle shops, particularly those that do custom work.

Plan Before You Place

Mounting the accessory needs some consideration, especially if the new gizmo dislikes rain, heat or vibration. The manufacturer will usually suggest an appropriate mounting point. If at all possible, follow this advice. Likewise, if the device needs to be insulated from vibration, believe me, resist the temptation to bolt it solidly to the frame just because you think it'll work better. Many high-current accessories require relays. Relays tend to be weather-sensitive, so mount them in an out-of-the-way, dry, secure area, like in the headlight shell, under the tank or seat or in a fairing, if possible. Of course, all terminal connections should be protected with dielectric silicone grease, especially if you're an all-weather rider. The same goes for any add-on switches. Mount them securely mounted and protect them from the elements.

No discussion on electrical installations would be complete without touching on fuses. Fuses are designed to sacrifice themselves any time the current load approaches dangerous levels, so the first rule is to never defeat their purpose by replacing a blown fuse with one carrying a higher rating. Rule number two is that any time an electrical accessory is added, make certain there is a fuse already in place or that one is placed somewhere in the circuit as close to the power source as possible. By locating the fuse at the supply end of the circuit, a short will cause the fuse to blow before the wire heats up and the circuit is damaged. If the fuse is located at the component end of the circuit, a short will burn the wiring between the source and the fuse before the fuse blows.

Speaking of shorts, it's always a good idea to disconnect the battery any time you're fiddling with the electrical system. By doing so you avoid big showers of sparks should you inadvertently ground a hot circuit. In a perfect world, we'd disconnect the battery, use our shop manual's wiring diagram to identify the correct circuits, then make the right connections. You and I know that in the real world we're going to power up the circuit, use our test lamp to make sure it's the one we want, then splice in our new wire. I'm not going to tell you I've never done it that way. But I'd suggest the following alternate procedure for those who don't want to do it by the book. With the circuit powered up, unplug the wires and use your test light to identify them, marking them accordingly. Once you've identified all the wires, disconnect the battery or pull the appropriate fuse before making the connections.

Lastly, bear in mind that any time an electrical accessory is added, draw on the electrical system increases. In some instances the charging system may no longer be able to keep up with the load. So choose your accessories wisely. Given the choice between a heated riding suit and 32 additional taillights, I'd be more inclined to pick comfort over custom.

For more articles on how to maintain and modify your motorcycle, see the Tech section of MotorcycleCruiser.com.

Tools typically needed for electrical work include: * Screwdrivers: Flat and Phillips head * Rachet * Wire cutters * Duct tape * Silicone compound
With the seat removed, the taillight's wiring connector was disconnected. Since it was under the turn-signal connections, those were also disconnected and placed aside. Typically, these connectors have an easily broken push-to-release tab, so be firm but gentle, and don't forget to take note of the wire's and connector's color-coding.
Without a wiring diagram handy, I had to resort to the old-school method of identifying the bike's taillight connections by probing them.
Unless you're a gambling man, pull the appropriate fuse or disconnect the battery before making your connections.
The fuse-box lid often identifies the fuse's and circuit's location.
Any time wiring passes through a drilled hole, it needs to be protected with a rubber grommet. Since the new wires must pass through the fender, the appropriately sized hole was drilled and a grommet installed to protect them from chafing.
To protect the wires from damage and create a neater appearance, a piece of heat-shrink was installed where the wires exit through the fender.
In a typical installation, the new wires can usually be run parallel to the existing harness and tie-wrapped in place. Following the Rivco instructions, the new running/brake lights' connections were spliced into the OEM harness using the supplied (red) crimp connectors. The modulator unit was tucked away safely next to the frame rail and plugs into the lights via the blue butt connectors.