Motorcycle Electrics, FAQ and ‘how to’

Motorcycle Electrics, FAQ and ‘how to’

Motorcycle Electrics – Tips & Tricks
By Curt at

Disconnect Your Battery

It’s a good rule of thumb whenever you’re working the electrical system to disconnect the negative terminal of your battery.

This will prevent a spark when reconnecting the battery. It will also prevent a path back to the battery should you accidentally touch a wire from the positive terminal of the battery to the frame or any other metal on the bike. Of course no one would ever do that. 😉

Power Output Versus Speed

Remember that your bike has a harder time providing power to the bike and your accessories when the bike is at idle.

When slowing down or stopping it’s a good idea to turn off any devices that require a high amount of current (like halogen lighting or heated gear). Your bike’s charging system is designed to provide power at running RPMs. If your devices are consuming more power than the bike can provide at idle, you are draining power from the battery.

Volts, Amps and Watts

This one seems to confuse people but there’s nothing much to it.

It’s called Ohm’s Law and he was a cool dude because he came up with a simple relation between these three entities of electricity — volts, amps and watts. When dealing with wiring you want to be concerned with the amount of current or power a device draws or consumes. That’s how you know what to use for a fuse and if the FZ-1 can handle what you’re trying to power. So here’s a rundown that will hopefully help.

Power is measured in watts. Current is measured in amps. Fuses are rated in amps. Your bike has a 12-volt system. Accessories generally give their power or current rating. Usually you’re concerned with how many amps the device draws but if you’re only given the amount of power used how do you convert to amps? What about if the opposite is true?

Just apply these simple formulas:

  • Power (Watts) = Current (Amps) * Voltage (Volts)
  • Current (Amps) = Power (Watts) / Voltage (Volts)
  • Example: Gerbing Jacket: 77 Watts / 12 Volts = 6.41 Amps
  • Example: Garmin GPS: 1.5 Amps * 12 Volts = 18 Watts
  • Example: PIAA 1100Xs: (55 Watts * 2 bulbs) / 12 Volts = 9.166 Amps

Ohm’s Law Calculators
Click to calculate for Current, Power, Resistance, or Voltage

If you don’t know what fuse to use it’s recommended to use a fuse that’s slightly above the amperage rating of the device. Remember that most fuses will operate above their rated amperage (sometimes up to 50% more). If you’re unsure, get a fuse close to the device’s current rating. If the device is operating normally and it blows the fuse then step the fuse up.

I don’t recommend this method but you can do it. It’s better to know what the manufacturer recommends.

Common Issues and Suggested Solutions

There are always issues as well as areas of concern with dealing with wiring.

Too Many Connections

Every time you make a connection it has the potential to fail for one reason or another. Keep your connections to a minimum. Butt splices to extend a wire isn’t a good idea if you can avoid it. If you do have to extend a wire consider running a new one or use a good butt splice. Posi-Locks are some of the best butt splices I’ve used. They require no tools, are reusable and make a very solid connection.

Poor Ground

When connecting any device there’s a flow of current from the positive terminal of the battery, through your device and then to the negative terminal of the battery (okay, all you electrical engineers just back off. You have to go one way or the other so just work with me). Where was I? Oh yeah. If there is a break anywhere along that path the device won’t work. When one device loses power most people check the fuse first and then look to see if the power connector is plugged in properly. If it’s not one of those, people get lost. A common issue is that the ground wire is not grounded properly. Make sure that the ground wire is touching bare metal, that there’s no corrosion on the wire/terminal and that it’s securely in place. This is a common problem (no pun).

Sloppy Crimps

Eventually you’ll have to crimp something while wiring. Crimps are evil things and they make poor connections unless they are done properly. If you’re going to use crimp-type terminals get the proper crimper. You can get the generic crimpers at any hardware store but these are usually not sufficient to make a reliable crimp that is going to put up with miles of abuse. Jim at has taken the time to write up an extensive tutorial on crimping. I recommend giving it a read and check out Jim’s products while you’re there.

The Fuse Myth

It’s a myth that a fuse is made to protect the device it is connected to.

A fuse blows when the amount of current it can handle is exceeded. The issue arises when the current is already flowing through the fuse before it blows (which means the device, or a wiring issue, is causing that circuit to draw more current than it should be). Since the current is already flowing through the fuse it is also flowing through the device at the same time. Using the proper amperage of fuse will protect your device but remember, the fuse will only blow when the amount of current the device needs is exceeded.

The fuse also has another purpose and it’s more important than protecting the device — the fuse protects your vehicle.

Remember, if the device starts to draw more current that means there is a short or a wire between the positive and negative terminals of your battery. The wire gets hot and draws an infinite amount of current. That’s bad and could cause a fire if there isn’t a fuse to protect the circuit. This is same thing circuit breakers do on power strips at home. They don’t protect your TV from a surge, they keep your house from burning down. If a surge or short causes the TV to draw a lot of current (which causes heat) it will blow the breaker so the power cord doesn’t catch fire.

Protecting your device is important but the fuse is to keep you from frying your bike or, worse, yourself.

Motorcycle Wiring How-To

See here for a more in depth article by Curt at covering the following topics:

How Much Power Do I Have?
How Much Power Can I Realistically Use?
Wiring Knowledge and Background
What Exactly is a Fuse?
Plan Before You Execute
Wire Routing and What to Look For
Making Good Connections
Crimp Connectors Drool
Locking Connectors Rule
Wire Taps
Adding a Relay (Switched Power)
Before You Power Up
Recheck and Adjust
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