Adding electrical accessories to your bike is an age-old custom for street and touring riders. Heated grips, fog lights, USB charging ports, GPS systems, sound systems, gear-position indicators and auxiliary brake lights all add to our comfort, enjoyment and safety out on the road. All of these devices need power, however, and it’s important that any electrical connections you make are done properly and that your bike’s charging system is up to the task.
Before you ask anything more of your motorcycle’s electrical system (it’s already supporting a headlight and taillight, fuel pump, gauges, an ignition system, and the occasional turn signal, brake light and horn) you’ll want to verify the health of your battery. A good place to start is by checking the resting voltage with a multimeter. Despite being a “12-volt” battery, it should actually show closer to 12.6 volts when fully charged, with 12.0 volts correlating to an unhealthy 50-percent state of charge.
Modern absorbed glass mat (AGM) and gel batteries have a lifespan of about four to seven years, so you would be wise to swap it for a fresh one if it’s getting on in years. If there’s any corrosion on the terminals, remove the battery and scrub the lugs with a wire brush and a one-to-one solution of baking soda and water. It’s important to keep those terminals nice and clean to reduce resistance to current flow.
Next, you’ll want to make sure your bike’s charging system is doing its job by checking the voltage at the battery with the bike running at about 3,000 rpm. You should see 14.4 volts or more. Verifying that your charging system has enough surplus wattage is a good idea if you intend to run especially thirsty accessories like head-to-toe heated apparel, but alternator output can be an elusive or nonexistent spec in the owner’s manual. Thankfully, most modern charging systems have plenty of strength to support your bike’s vitals plus another 100 or so watts’ worth of accessories.
If your new farkle is a factory part, it’s possible that the manufacturer has already provided an electrical plug to power it. Check your fuse-box lid for an “aux” circuit and reference your owner’s manual for the plug location. (Hint: It’s often under the seat or behind the dash.)
Without a factory connection, the easiest way to power your new gadget is to tap right into the battery. While this may be convenient, bolting up to the lugs poses two major problems. For starters, there’s only room for a few ring terminals before those battery bolts run out of thread, so if you’re aiming to add more than one or two accessories you may not have room. Second, there’s the very real possibility of draining every available volt out of the electrolyte if you were to say, leave your heated grips on accidently after parking the bike for the night. You think you’ll never forget to turn ’em off, but when you eventually, inevitably do, your battery is going to be as useless as a brick when you come back to the bike.
A better alternative is to use switched power, so current only flows when the key is on. Tapping into the headlight or taillight wiring will work for low-draw items like a cellphone or GPS charger, but if you ask too much of an existing circuit you’re liable to blow a fuse.
So why not run dedicated, switched, fused circuits for accessories? The best way to do that is with a relay and a fused distribution block, both of which can be sourced at your local autoparts store or purchased as a single, integrated unit from companies like Twisted Throttle, Aerostich, Centech and others. With a relayed setup your accessories will only pull power when the key is on, and using a distribution block allows you to easily add or remove accessories, consolidate wiring and keep your battery top tidy.
However you decide to pull power, it’s critical that the new component be fused to protect both the accessory and your bike’s wiring. Push too much current through an unfused connection and things may melt or even catch fire. Good grounding is another key consideration for any electrical component. You can connect to the main chassis ground, tap into the wiring harness or connect directly to the battery’s negative terminal.
Speaking of the negative terminal, disconnecting it is the first thing you should do when working on your bike’s electrics and the last thing you should reconnect when you’re done. With the negative terminal unplugged there’s no risk of a sparks show if a live wire touches the frame or your wrench slips while fiddling with the positive terminal.
Finally, it’s important to ensure that any electrical connections you make are secure and well insulated. Shield bullet and spade connectors with rubber boots or plastic covers, and use heat-shrink tubing for any soldered joints. Don’t be tempted by electrical tape — the adhesive often fails after just a short time, exposing wiring and making a sticky mess.
Electrical accessories can keep you warm when the weather is miserable, provide a soundtrack for your journey, make you more visible on the road and improve your riding experience in numerous other ways. Outfitting your motorcycle with the latest farkles is a time-honored tradition, and if you follow these tips and precautions you’ll be powered up in no time.