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Hey guys,

About to drive home for lunch today and my bike started with a little trouble. (Normal for my bike-carbs need cleaned.) It died and I tried to start it I got nothing, Smoke started pouring out from underneath my seat. noticed some sparks and a small flame. It eventually went out.

Here's what I'm dealing with now- The fire melted the negative terminal and one of the ground wires leading to the frame. Now there could be an obvious reason as to why this happened- My bobber seat pan is made of metal and it sits on top of the frame directly above the battery. Could that have shorted the battery out or was the negative terminal screw loose? Any ideas? I'm obviously going to replace the battery and the melted wiring. As well as get a new bobber seat that isn't metal on the bottom.

Need help from you electrical gurus!

A loose connection or corroded connection at the battery can cause extreme heating because the alternator is dumping maybe 20 - 30 Amps into the battery to recharge it. A bad connection causes resistance which makes power dissipation which makes heat.

doesn't look like a seat pan short because that wouldn't have gone through the wires as shown in the picture.

I don't think that was caused by a seat pan short because you burned up a small ground wire. I can't tell from the diagram (which has the negative and positive labels switched at the battery!) which ground wire it is that burned up because one of them has been cut and spliced. It looks like the bottom/lower one is the wire that started the fire since it also melted into the battery. It could be something relatively simple like a high resistance connection where it connects to the battery, or some other device on the bike could be allowing far too much current to ground.

I'd start by checking if all of the fuses are the correct size and by tracing where that wire connects to the bike. Does it go straight to the frame or does it meander through the bike connecting to a bunch of other things?


*EDIT*
Thinking about it more I might be wrong, if your seat pan connected the + terminal to the frame the return path for current would be sort of spread across the ground wires, perhaps the smallest one would burn first. Is there any evidence of rubbing or shorting on the bottom of your seat pan?

zero10 wrote: *EDIT*
Thinking about it more I might be wrong, if your seat pan connected the + terminal to the frame the return path for current would be sort of spread across the ground wires, perhaps the smallest one would burn first. Is there any evidence of rubbing or shorting on the bottom of your seat pan?

Good analysis. No fuses blow because the ground side is not fused. This type of short can only happen when the short occurs before the fuse box, as in, when the frame comes into contact with the battery positive post. The common result is melted ground wires.

Most of the guys I ride with have some sort of custom or another, so I see this more often than I'd like.

You sort of have to inspect all of your wiring. There can be hidden melted areas where the ground and positive are in danger of coming into contact. This can be the source of mysterious blown fuses in the future.

The wire that had the most damage is the black ground wire off of the negative terminal in the picture. It doesn't meander through anything. Straight to frame ground. But, something I did notice is the previous owner put another ground cable to the - terminal. Seat pan just had some battery and melted plastic juice on it. No visible short damage.