Farmall C 3 Wire Alternator with Solenoid Backfeed

Hey all, Back again with questions about the C I recently acquired.

This tractor has been converted to 12V with a Delco 10SI 3 wire alternator. The PO also installed an automotive style key start ignition switch with accessory feature, as well as a solenoid.

In an earlier post I had mentioned that alternator was not charging. I took it in to a local part store and they bench tested it for me and confirmed it was dead. I purchased a replacement 3 wire and installed it back in the tractor. Now it is charging perfectly.

After shutting down the tractor and doing some more work on it, I happened to touch the alternator and found it to be hot to the touch, almost too hot to keep my hand on it. So something was apparently back feeding power to the alternator. I promptly unhooked the pos battery cable and let things cool off.

In the mean time I inspected the wiring and all seems to be ok, but I did notice there does not appear to be a Resistor, or diode, or dummy light coming off the #1 terminal on the Delco. It just goes straightto the ignition switch. I will admit I have never wired a solenoid so I am not sure about the wiring on that, but all seems to work as it should. Is my problem that there is nothing between the #1 and ignition switch?

What terminal on the ignition switch is the wire from the alternator's #1 terminal connected to, and does that terminal power down when the key is switched to the "OFF" position? (If nothing else is connected to the "ACC" terminal that would be the best place to connect the "excite" wire.)

If it does, likely the internal regulator in the alternator has failed and is feeding current to the rotating field after shutdown.

OR, it may have nothing to do with the #1 terminal or the wiring, a diode(s) in the rectifier may have failed.

All that being said, it's a good idea to have an "idiot light", a diode, or a resistor in the "excite" lead to limit current from backfeeding though the voltage regulator from the diode trio. This system was not designed to output current from the alternator and if more than a couple of Amps flow out from the #1 terminal the diode trio and/or the voltage regulator will be fried.

Here's another scenario that can happen that is prevented by having one of the previously mentioned current limiting devices in the "excite" circuit.

<img src = "https://www.gondtc.com/~blweltin/Bob/DelcoSIA1A.gif">

<img src = "https://www.gondtc.com/~blweltin/Bob/DelcoSIB1A.gif">

I would have to look again which terminal the #1 runs to on the ignition switch but I beleive it is connected to the top terminal, if that tells you anything.

The head lights are connected to the Acc terminal as they will work when the key in in the "ACC" position and will not work when the key is in the "Off" position.

This is a brand new from the box alternator so it would be hard to believe it has failed already (though I know it can be possible) It does still charge as it should.

#1 terminal needs power when the key is "on" but must be isolated from the ignition circuit. A diode works. In your case, it is easier to
just wire #1 on the alternator to the ACC terminal of your switch and do not put anything else on ACC. Make sure everything else that needs
power then the key is on is wired to the IGN terminal. This works great and avoids the need for a diode or resistor.

The amount of current going into the alternator (if left on is not enough to heat it up. A bad diode trio, or a bad bridge will do
that. I suggest taking it back. Alternators do get pretty warm, but after 15 minutes or so should be easily touched unless
getting hot from an internal fault. Alternators are connected directly to the battery through wiring, or an amp gauge (which is a
different "wire" so it will always be electrically hot at the output terminal. Jim

I dug more into the wiring this weekend and found that the #1 wire from the Alt was wired to the Bat terminal on the ignition switch. The #2/Bat wire from the Alt were wired to the Amp Meter. So both terminals on the Alt were receiving constant power.

I switched the #1 wire from Bat to Acc, as JDEM had suggested, and my problem went away and it is charging as it should.

Question though, is there any reason I could not wire the #1 to the Ign terminal on the ignition switch? I ran across a post where someone had done that instead of Acc, and said it worked fine?