How to figure out what size fuse to use

I'm running a 4 fuse system but still have 2 open fuses on the buss. I don't know what size fuses to use so I've listed what's on each one below. I could split the "lighting" relay into 2 if needed like head/tail light and turn signals/gauge pod. I've already put a lot of time and cash into the bike and don't want to catch it ...or myself.... on fire. The relays I'm using are 40 amps each. Someone telling me what to use is okay but I'd like to know how to do it myself.



1st fuse lighting - 4 incandesant turn signal bulbs (23 watts each but only 2 can run at a time), 35w HID headlight, LED tail and brake light and KOSO RX1N gauge pod (unknown power draw)

2nd fuse relays - ignition relay, light relay and starter solinoid

3rd fuse ignition - 3 ohm dyna green coils and dyna S ignition

4th fuse - horn

size the fuses to wire gauge/size

When it comes to fuses, it really depends on what the wiring on a particular bus can take. The components will draw whatever current they need and the wires just have to put up with it.

You could throw a good amp meter in the circuit and turn everything max, then select a fuse just higher than that, provided the wires dont get too hot :huh: keep an eye open!

Stock is a 30 amp fuse for starter/main.

The rest at 10 amp should be fine.


Correct me if I'm wrong boys

GL!

I agree with TeK9

The only thing I would really worry about is your gauges, and that probably has an internal fuse for protection. The owners manual would be a good place to check about that.

On the second fuse, it's just supplying the coils on the two relays right?

Unless you have a monster horn, you could put that on one of the other circuits and use the 4th slot as a spare fuse holder.

EDIT: Sorry on the spare fuse thing didn't catch that you still have 2 open slots.

In general, the fuse rating needs to be about 1.5X times whatever the MAXIMUM continuous current for that branch will be. Wire gauge is a separate issue, you need wire thick enough to carry that current without significant heating.

Most motorcycle wiring is in a bundle/harness/loom that will tend to heat up compared to a wire that is not bundled together. Always allow a little "Fudge Factor" (I.E.if 16 gauge works, go for 14 gauge).

American Wire Gauge (AWG) works backwards to what people think, that is an 8 gauge wire is smaller in number than a 14 gauge, but is many times larger in conductor size.

Looking at my bikes fuse block, I see that 12 gauge is used for the 30 amp circuit with either 16 or 14 gauge used for the 10 amp circuits.

MFolks wrote:

Most motorcycle wiring is in a bundle/harness/loom that will tend to heat up compared to a wire that is not bundled together. Always allow a little "Fudge Factor" (I.E.if 16 gauge works, go for 14 gauge).

American Wire Gauge (AWG) works backwards to what people think, that is an 8 gauge wire is smaller in number than a 14 gauge, but is many times larger in conductor size.

Looking at my bikes fuse block, I see that 12 gauge is used for the 30 amp circuit with either 16 or 14 gauge used for the 10 amp circuits.

AWG16 for 10A makes me a little nervous..... but I think that is still the code for homes. I think AWG14 is code for 15A and AWG12 is code for 20A 115VAC wiring. I agree always make it thicker than you need. I also prefer teflon jacketed wire as it is more resistant to cut through.

When I made test equipment and cables at General Dynamics/Convair in San Diego, the wire spec's were for Teflon insulated, silver plated copper wire.It was easy to solder with no worry about insulation creep back or burning.

It was pricey, of course, a Gov't contract with money with almost no limit.

When I was in the USAF, I remember the F-4 Phantom II's had Teflon wiring in the weapons pylons. All white wires with heat shrinkable sleeves for circuit identification.

Telfon in a wire bundle is pretty stiff and tends to hold what ever position it was in last.

kz1000 80s model are 30 amp main,10 amp everything else. I figure that is plenty given that these old bikes are 30 years old now and are still functioning with the original wiring and in my case some of the original fuses.bj

I used 14 and 16 gauge for everything but the coil power and headlight using 12 gauge for just those two items. The 16 gauge has this printed on the wire - cerro vinylon-a 16 awg flexing(ul) tffn or mtw or awm cr2 600v. The 14 gauge has this printed on the wire - e102470 s (ul) 14 awg mtw or thhn or thwn gasoline and oil resistant II or awm 1316 or 1408 600 v vw-1. I will run a 30 amp for the ignition and 10 amp for everything else.

Thanks all,
-Cru