'78 GS750 Electrical Problem

[bj]

Hi folks. I need some help with this one. I torn down and rebuilt my '78 GS750 this past winter, everything but the engine was completely disassemble and either cleaned, replaced or power coated. I checked the wiring, cleaned and/or replace all connectors and rewrapped the wiring harness. The only modification from stock is a Electrix R&R with the headlight switch wiring bypassed. I've done several 1000 mile weekend trips on it since with no problems at all.

This week the single main fuse popped on me at a stop stop sign, while the brake light and right turn signal were on. When I checked the fuse, the plastic holder was partially melted! I put in a new fuse and the bike ran fine, no problems getting home. I replaced the fuse holder yesterday with an automotive type blade fuse holder. Today on a short test ride the fuse popped again and it was very hot. It almost looked like the fuse melted rather than blowing.

I need to get this figured out quick since I'm supposed to ride from Baltimore to the AMA Vintage Days in Ohio this week.

Any ideas where I should start looking? What would cause heat like that in the wiring? Any help would be greatly appreciated.

[duaneage]

Obviously a short circuit somewhere.

Try this:

Get the bike on a battery charger/booster that can power the bike. Those chargers can deliver up to 10 amps. If you do have a short circuit the battery charger can take it better than a battery and it won't damage the battery.

Remove the fuse and wire a light between the fuse blades. You can use a turn signal, or even a voltmeter for this.

Wiggle the wires around with the key on and if the light comes on you have a short circuit to the frame. Then it is a matter of finding what is pinched where. You probably made a simple mistake in routing the wires and something is rubbing a sharp piece of metal somewhere, or else water got into a bunch of stuff and it it is shorting out.

[KEITH KRAUSE]

Burning insulation is either a poor connection nearby or too many amps (ground/short) passing through the wire.
If the harness is factory, you need to check for evidence of grounds or shorts between wires and between wires and other parts.
I assume the main fuse you're using is the correct size?

[bj]

Thanks for the suggestions guys. Nothing like working under pressure, especially when you're working with something out of your comfort zone.

[BadBillyB]

Seems to me that the only circuits that go through the main fuse (without going through a smaller or other fuse) is the charging system and the ignition switch. Check your charging system voltage with the engine running. Check the wiring to and from the ignition switch and R/R.........BadBillyB

[Pearson]

Didn't I read in your "Restification" blog that you had to work on wires in the rear turn signal and brake light area? Might want to revisit those. FYI if you're not using heat shrink for rewiring projects, I'd highly recommend it. Keep us posted.

[bj]

Found it.

A volt meter connected in place of the fuse showed about a 1 volt draw with the key off. After 5 hours of testing, disconnecting and reconnecting wires, I narrowed it down to the orange wire from the ignition switch. Replaced the switch with a spare and no more 1 volt draw. Everything seems to be working properly and there's no more heat around the fuse.

Thanks for the help everyone.

[duaneage]

Probably an internal short on the switch. Putting the voltmeter across the fuseblock is an unconventional technique but it works, that's why I suggested it. It is safer than checking current draw because the meter provides a resistance to protect the battery with.