TOPIC:

First off let me explain the bike was completely rewired before i bought it. All the wires are red so it makes it difficult to follow.

First issue is when i turn the ignition on the main wire at the fuse box get real hot without even cranking the bike. Some of the plastic is melted around it. Any ideas on what could be causing the heat???

The bike is a 1975 Z1B.

did they use large enough wire size?

too small of wire to carry load,bad ground,bad connection some place or maybe a bare wire touching just eough to cause a load but not short.id say start disconecting things and start plugging tem back in one at a time till the wire starts getting hot then start from there.

Check for resistance between each connection point and ground, then check the resistance between each connection point.

While you're at it turn the bike on for a second or so and check the voltage (or voltage drop) at each leg of the wiring.

I suppose another way to go about it is to meticulously label every connection and slowly unplug them until the main fuse stops getting hot. That would give you a starting point.

Hey wait, can you still get harnesseses for these?

Yeah i looked it up you can get brand new ones for $125. Id like to avoid it but it seems like it might be unavoidable at this point.

Avoidable, but it might save enough time and frustration to make it worth it.

I got one at a wrecking yard for much less. Is there a wrecking yard near you?

Yeah there are a couple junk yards around here with lots of bikes.

PhildoBaggins wrote:

First off let me explain the bike was completely rewired before i bought it. All the wires are red so it makes it difficult to follow.

First issue is when i turn the ignition on the main wire at the fuse box get real hot without even cranking the bike. Some of the plastic is melted around it. Any ideas on what could be causing the heat???
The bike is a 1975 Z1B.

More current is flowing in the wire than it's diameter can handle.

ALSO: the fuse itself is probably getting hot and the heat from it is being conducted out into the wire connected at the fuse box.

Is it getting hot just at the fuse box? Or is the wire hot all along it's length? If it's getting hot only at the fuse box, you likely have a poor contact at the fuse clips as I had on my 650. I fixed it by replacing the fuse box with a blade type box. Works MUCH better now. Lights are brighter, flashers are faster, etc.

Understand that there is voltage at this point and the fact that the wire goes to the ignition switch doesn't have a lot to do with the heat. The wire coming off the main fuse should have 12VDC on it at all times because it does feed the ignition switch. It is usually 12 or 14 gauge wire I believe and if a skinnier wire is used, it WILL heat up and melt the fuse holder. A cold or weak solder joint will also do the same thing where the main wire is soldered onto the fuse holder. Buy a modern blade fuse holder and get rid of the old one and install a 12 gauge wire from the main fuse to the input of the ignition swtich.

I would get an AMMETER and measure the current in the wire first thing. Fuses running at about 80% or higher of their rating get hotter than hell. Before rewiring, find out what currents are going where and why, and compare the amount of current to the fuses in those lines as well as the wire gauge. That may nail down the problem.

BTW: old fuses go bad, so replace the hot one with a new one of the correct rating before going nuts on repairs.

I measured current once a few years ago and as usual didn't take notes, but I think this wire to the 20A fuse flowed around 8A max with lights on and engine off, less when engine running. The fuse runs real warm even at this amperage, less than 50% it's rating. The reason is the fuse clips. Corrosion over time makes all the connectors and the fuse clips also to get a less than intended connection and warm turns to HOT real fast.