[harshweld]

1981 CM400

Previous owner rewired the bike without a fuseblock, turn signals, or a horn. There is only the headlight and a small aftermarket taillight wired up on the bike.

Looking to add in small bladed inline fuse to circuit.

Does location matter on a circuit, as far as the fuse goes? Or can I just add one directly to the hit wire to the headlight, and just tuck the fuse inside the headlight housing?

How much total amperage would I be drawing,considering it’s only a headlight and small LED taillight?

Bike is also completely rewired with black 18 gauge wire, so color references are out the window.

 

[Rod Fryatt]

As the fuse is to protect the battery from any short circuit in the wiring it should be as close to the battery as possible. Inside the headlight would not be a good idea.

15 amps should be OK at a guess but I'm sure someone will be able to quote a correct figure.

 

[JamesPal]

I agree with Rod about the location. You want it as close to the battery as possible. The least length of unprotected wire the better. I would not ride the bike without a fuse. It is a fire trap. Here is a simple blade fuse. You could just splice it in between the positive battery terminal and the bike's electrical system. Use quality crimps and don't have the splices under tension. You might consider tying the wires to the frame so they are supported. Remember, if the splice fails the bike won't run.

 

[Sonreir]

Sorry, gents, but I need to step in and make a few corrections.

1.) Fuses are primarily to protect wiring, not batteries or components. Shorting most commonly found gauges of wires across a battery will result in no damage to the battery at all, but the wires can and will melt. The thicker the wire, the more likely you are to damage the battery, but this usually doesn't become an issue until you start hitting 10 gauge or thicker. Any thinner wire will quickly fry with the amount of current an automotive or motorcycle battery can pump through it.

2.) The location of a fuse within a circuit can be important, but only if you experience a short in the wire after where the fuse is located. The CXes (and other models, too, probably) had their fuse box located on the upper triple. Generally, failures of individual wires are rare unless they haven't been properly routed. You want to ensure you're fusing as many connectors and components as is possible. I like to locate my main fuse right off the battery positive terminal, on the wire that leads to the ignition switch. On the CM models, the main fuse is usually part of the solenoid.

15A is the usual size if you're going with only one main fuse. With only your LED headlight and tail light, 5A or 7.5A might be possible. Your ignition system is CDI and unfused. It gets power directly from the alternator, so you don't need to account for any current from that system. Make sure your regulator/rectifier is up to snuff. It's going to be shunting a lot of power to ground because the rest of the load has been lessened.

Generally, the size of the fuse is determined by the smallest wire gauge it is expected to be protecting. If you're pulling more power in your entire system than what can be handled by the smallest wire, you should put separate fuses on those smaller-gauged runs.

 

[Rod Fryatt]

Quite right, muddled thinking from me

 

[harshweld]

Thanks for the input, guys! I’ve decided on the 15 amp single fuse idea.