This is a follow-up to my recent posting, "battery drain." It concerns my 1941 Farmall A.
I removed the electrical box to paint it. Upon reassembly, the problem surfaced.
I just had a friend over, who is competent with electrical circuits and we did some work but could not solve the problem. I have the optional headlights and taillight on my tractor.
Here is the problem: when the switch is in the low charge position (full counterclockwise), the ammeter shows a charge. When the switch is turned to the high charge, dim lights or bright lights position, there is a full discharge shown on the ammeter. It pins immediately to the minus 20 position. We are supposing a short between two wires or a ground between a wire and the tractor frame, but we are unable to find one. At some point, we had some overheating in the box and even some smoke in the box. When we have the battery ground wire off of the battery, put the switch to the low charge position and then reattach the battery ground wire to the battery, there is NO arcing. When we have the battery ground wire disconnected from the battery and put the switch to any of the high charge, dim lights or bright lights positions and then reconnect the battery ground wire to the battery, we get some arcing. We are wondering if I caused damage to either the switch or some other part of the electrical system when I messed with my re connections and especially, at one point, turned the switch to various positions when I did NOT have the ground established because I did this when the electrical box cover was NOT attached to the electrical box.
Thanks for any input. Tom in Iowa City.

Sounds to me like you've got some wires swapped around on the switch or it is internally defective.

You've for sure got a short somewhere and it sounds as if it's in the charging circuit. Not exactly in the order you asked, but here's some thoughts.

Smoke in the box -- it's definitely a sign of something hot in there, but not necessarily a problem. I've had them do that when they haven't been wired up for some time and it was the heat burning years of crud off of the field resistor. Still, it could also be caused by your short.

The switch -- I doubt it's the problem, but couldn't eliminate it. I'd open it up last. If you do, you'll see why I doubt it as the problem. It's ungodly simple. Basically a brass or bronze disc that turns to make contact in various with the inside of the various contacts you see on the outside. It's held in place by a large simple spring. It's possible that a piece of the spring or the the disc has broken off and is floating loose but, like I say, it's unlikely enough that I'd check it last.

Here's how I'd go at it. Disconnect your battery, pull the face off of your panel, and disconnect every small wire you have on both ends, from the lights, the ammeter, the switch and the generator. Then use an ohmmeter to look for continuity to ground. You shouldn't find any. If you do that wire is a problem, but check all the others, too, in case they've shorted to each other as well as ground.

To my mind the two most suspect, because the problem is occurring whether the lights are on or not, are the wire running from the BAT terminal on the relay to the ammeter, and the wire from the field stud on the generator to the switch. If you have a starter, you should also pay attention to the wire from the ammeter to the hot stud ont he starter. Everything else, other than light wires, is basically short jumpers that should also be checked out.

Ifn you have a short there will be fire or smoke first. When you got the tractor it worked what did you do wrong. Your friend doesent know how the charging system works on an A Farmall or he would have made it work. Do you need me to come up and get it rite. gene

You have the wire that supplies the lights hooked to the terminal that the field wire is supposed to go on. The terminal is direct to ground when on all but the L position, and Ill bet the resistor is toast. Please read the previous post I put on the original thread. Good luck. JimN