Wiring a Sidecar
by Kevin Mahoney, Classic Motorworks / Cycle Sidecar
Wiring a sidecar is a fairly straightforward operation. Fortunately, the only chips in a sidecar are most likely in your picnic basket and you will be having them for lunch!
The information in this article assumes that you have some very basic knowledge of electrical theory and are somewhat handy. We have seen all sorts of things wired up in sidecars including automotive batteries, enough lights to shame a small Las Vegas casino, radios, spotlights, loudspeakers and even sub-woofers. Basically the only limitation is the output of the alternator on your motorcycle. While some smaller bikes are more limited, some of the new larger bikes have more electrical capacity than my 1972 pickup. It is worth a trip inside of your owners manual to determine the wattage (or a close approximation) of the electrical gear that is already installed on your bike. Headlights, taillights, ignition system etc. Don’t forget to account for things like heated clothing. Subtract whatever number you come up with from the capacity of the charging system and you will have a good idea of how much extra equipment you can add.
Most people are really only interested in adding a few lights to their sidecar and generally low wattage ones at that. Let’s say for example a taillight/brake light combination, a small wattage marker light on the top of the fender and a turn signal.
The first step is to decide where you want to mount the various lights. This will usually require some drilling. When drilling for the light mounts don’t forget to drill a hole for the wires of your device. Allow extra room for a rubber or plastic grommet.
Step Two is to plan your installation. The first thing is your choice of wiring. You can buy a pre-made wiring harness such as the ones we sell or make your own. I have seen people make them from scratch or even use a trailer wiring harness as beginning. You generally have to choose which size of wire to use. Wiring is a case where size does matter! Wire is sized by gauge, the smaller the number the bigger the wire. The bigger the wire the more current if can carry safely. Common sense goes long way here. As a rule of thumb, I go with one wire size bigger than the wires that come from the device. On the question of color there are two schools of thought. If you use common colors for different things like red for a hot lead and black for a ground lead it may be easier to trace them later. On the other hand using wires of the same color can be more visually pleasing.
The next step is to determine the routing of all the wires. A fundamental first choice is how you are going to ground the system. Electricity needs a complete circuit from the positive terminal on the battery (unless you are working on an old Vintage bike in which case the ground may be the positive lead), to the electrical device and then back to the negative terminal of the battery. The ground wire on your battery is frequently run to the frame of the vehicle. You can then use the metal of the bike as one big ground wire. For example, to make a taillight work you would only have to run one wire to the bulb. The other wire coming from the bulb could then be attached to the metal fender to complete the circuit. This is a simple time tested system and uses less wire that running a ground wire back to the battery from each device.
There are some pitfalls to be aware of. Paint, plastic, rubber, rust and powder coating either won’t conduct electricity or are very poor conductors (rust).
So when planning your grounding scheme be careful not to let any of these things get in the way. Some 2000 model year Royal Enfield’s came from the factory with powder coating over the lug on the frame that the battery ground was attached to. The result was predictable, bad grounds and electrical devices that didn’t work properly. One minute with a piece of sandpaper removing the powder coating and took care of the problem. The reason I mention this is that you can rely on the steel attachments between the sidecar and the motorcycle to act as a ground. However experience has shown me that it is good practice to have at least one good wire connection between the ground of the bike and the steel of the sidecar body or frame. If you have a fiberglass sidecar you have another dilemma as fiberglass won’t conduct electricity. In this case you could perhaps direct your ground connections to the steel frame of the sidecar and then to the motorcycle.
I would now loosely mount each of the lights you are intending to wire to the sidecar. Then lay out the wires that will be required to complete each circuit. You must determine where on the motorcycle you want to tap into the motorcycles electrical system. I suggest that in the case of the taillight you tap into the wires leading to the bikes taillights so that when you turn on the light switch on the bike it will also power the sidecar light. This also normally puts the sidecar taillight on a fused circuit for safety. If you are powering a device directly from the battery I suggest the use of an inline fuse to protect the circuit from overheating and even burning from a short circuit. If you are installing a turn signal you may want to run the wires from the old signal on the bike which you have just moved or relocated. When laying out the wires be sure to place them out of harms way, free from chafing against a moving part like the tire inside the fender etc. Be sure to use a grommet wherever a wire has to pass through a body panel or anything else that could cut through the insulation later. Be sure to clamp the wires or wire tie them solidly to the sidecar so that they do not move around once they are installed. If you are using a pre-made wiring harness the wires will be neat and clean, if not consider wrapping them with electrical tape or shrink tubing to keep them together and neat looking.
Before we tie everything together you have to decide about connections. It is a good idea to consider that you may want to remove the sidecar at some point for one reason or another. To make it easy you should include some disconnects somewhere between the bike and the sidecar. I have seen people use a trailer wiring harness connector or several individual connectors. Consider how weather proof and strong a connector is before you decide which type to use. A little dielectric grease can help weather proof a connection so that it does not corrode over time.
Now it is time to wire up each device. Again there are a multitude of connectors available to do the job, but butt connectors that are crimped on are a good way to connect two wires. They are available at any auto parts or hardware store. A small kit with a crimper is a good investment.
Consider where they are and how exposed to the elements they are. This is also a good place to consider some dielectric grease or shrink tubing to protect them from future corrosion.
After you are finished, turn the switch and admire your handiwork, with any luck at all everything will work and be ready for years of service.
Please give us a call with any of your sidecar questions.