Electrical short - hot wire from battery to switch

[Lonnie]

On a local club ride today, riding a knucklehead (pre-47) an interesting thing happened. We stopped for gas and when I switched it off, I saw heavy smoke coming from the top of the seat post area, followed by heavy smoke from under the dash cover! I jerked the negative ground wire in two to break the circuit. Got the bike home and have just started taking it apart and I do believe I need some advise. No, it is not for sale and yes, I know I need to install an inline fuse and will do so.

The bike is restored with cloth-covered wire following the wiring diagram in the shop manual The red wire from the battery to the terminal under the seat is fried as is the red wire in "Cable A" to the ignition switch. From what I can see no other wires are damaged but I will not know for sure until I take off the right tank in the morning.

I do not see any indication that these wires grounded out but the insulation is burnt off in places so I can't be sure.

This whole deal is interesting, to say the least, since on another ride awhile back in the summer this bike also quit, start sputtering then died. It seemed the battery had lost a cell, could not recharge much over 4 volts so I replaced the battery. Now, due to the dead short this new battery is completely dead and I am recharging it on a trickle maintainer-type charger.

Could there be some connection between these two occurrences? Could I have a generator issue (6V, 32E rebuilt when the bike was restored) or a relay issue (solid state)? Or is it likely that is just coincidental and not logical that there is any connection between these two events?

Any ideas before I replace this wiring and have another wiring fire? Any advise or pointers would be most helpful!

[Sargehere]

The place for that in line fuse is the battery hot wire, the one that fried first, between the battery and the hot terminal at the seatpost. Would have saved you some fried wire, in this case (don't know how many people I've seen put a fuse in the ground wire to the battery, and that's the last thing to burn). You have a dead short ground, which you'll find when you pull the tanks off, no doubt. The previous episode could have been a precursor to this one; a short, but it fixed itself: wire moved when it heated up, or burning insulation healed itself over somehow. Now you've gone and done it, Lonnie. You're going to have to fix it right!
I don't expect you've done any permanent harm, tho. Just some wire that rubbed on something and went to dead ground. Rewire it by the factory and you'll be all right. It doesn't have anything to do with the generator or regulator, I don't think. You'll find the ground when you trace the burnt wire to whereever it stops being black and crisp. Good luck with it!

[Lonnie]

Thanks, Sarge. I used to do the inline fuse thing "back in the day" but have not done so on these recent restorations, mistakenly thinking nothing would ever happen. Ignorance is bliss, I suppose.

The wire fried all the way back to the ignition switch. Can't see where anything is touching there. However, those cateye dashes don't leave much room around the switch so I'll check closely there. My worry is that I don't find the problem, in which case I'll just have to replace the burn wiring, probably all the wiring in Cable A (the loom along the top of the backbone) and try again. I'll leave the right tank and dash cover off for a while. That should be a good conversation starter.

[Sargehere]

Consider rebuilding or replacing your switch, Lonnie. They're easy enuf to rebuild. The I've seen old Harley switches just "wear out," and get so loosey-goosey they made
"unintended contacts." The fibre contact plate can literally fall apart, the metal contacts coming out of place, and you don't even notice. Sounds like you just have a ground somewhere around the perimeter of the contact plate. Good luck!

[MJW]

I've had the dash cover make contact with the terminals on the switch, when I first got the bike. The P.O. had done a lot of barnyard engineering which finally led me to a complete tear down and re-build, sadly at that time I didn't know the difference between a re-build and a restore. Mike

[Perry Ruiter]

If you're burning the wiring you've got a dead short. Typically a generator wouldn't have such a direct path to ground as to cause a dead short. If the burning stopped at the switch that's what I would suspect. Take a ohmmeter and check for a path to ground from the terminal where the wire from the battery connects (with the switch off there should be none). As you note it could be the cover moved slightly and touched. You got the switch assembled correctly for a catseye (three terminals to the front of the bike not the rear) ... Perry

[Lonnie]

Yup, the three terminals are to the front. Have had no trouble for over 2,000 miles. I reckon I'll rebuild the switch, replace the hot wires and the Cable A assembly and take it from there. I'll try to see if I can purchase just the Cable A run without buying the entire harness, if I can't I'll have to make one but it won't be exactly correct in appearance. I'll run it without the dash cover and the right tank for awhile to better see what is going on - plus it'll drive the late model guys bananas.