Troubleshooting 12V conversion with externally regulated GM alternator

From what you describe you simply need to connect from terminal #4 ( the one you've been using to get it to charge ) to a lug on the ignition switch that is only hot when the key is "on". This lug must not be the same one that feeds to the coil / distributer. The two items must become electrically separated when the key is turned off otherwise the alternator keeps feeding the distributer circuit once the alternator has begun charging. If the ignition switch has an acessory position that is where you connect it. You can leave the bulb out of the circuit since you have a voltmeter to work with. The purpose of the bulb is to add resistance to the circuit enough to drag down the charging system when the engine is turned off so you don't have the run on problem. GM alt circuits use a dash bulb for that reason along with indicating the system isnt charging. You should be fine without it. Hope this gets you pointed in the right direction, otherwise you seem to have a good handle on it.

It is currently connected as follows

F terminal on the regulator to the F terminal on alternator "2" terminal on the regulator to the "R" terminal on alternator "3" terminal on the regulator to the "bat" terminal on alternator and

• battery terminal The case of regulator is grounded, as is the alternator ground lug (and just to make sure I ran an extra ground wire directly between the two).

Various sources (internet, local parts guys, etc) seem to indicate that the above is correct.

I'm assuming that the problem is with terminal "4". This was hooked to a wire coming out of a tangle that seemed to initially come from an ammeter. 12 Volts never appeared on this input, and the tractor did not charge. When I jump this to 12 volts, the tractor charges. (I see 14 or so volts across battery whereas I see 12.9 when tractor is not running with a fully charged, newish, battery). Of course, if I do this I CANNOT TURN IT OFF. The tractor keeps running when I attempt to shut it down.

Same wisdom sources indicate that I should put a warning light in series with this (so instead of connecting terminal 4 to 12 volts, run it through a light first. A #161 was specifically recommended, so I soldered a pigtail to a #161 and put it in line (measures 9 ohms across my bulb+pigtail before I put hook it up). If I turn on the tractor, the bulb glows, but the tractor does not charge. If I jumper (bypass) the bulb (I'm back to where I was before, and) the bulb goes out, the tractor charges but won't turn off. If I TEMPORARLY short around the bulb, the bulb goes out (duh), and when I remove the jumper it STAYS out, and the tractor keeps charging, and now I can shut it off.

The question: I'd like the tractor to charge w/out going through these hoops. I'd also like to be able to shut the tractor off. (I realize I can rig up a toggle switch or relay and get this to happen, that's not what I'm asking. Running this terminal to the starter relay (only hot when cranking) doesn't work either, the connection gets real hot since the starting motor acts as ground when not engaged). I also tried tying terminal 4 to the bottom of the ballast resistor, with the same effect (charges, but can't shut off).

Any solution? The previous/current owner has another alternator which checks out fine (according to a local shop), I might swap that in just to see what happens. The voltage regulator is new (and the old one checks out fine). The guy I'm buying it from replaced parts trying to track down the problem. The tractor is at my house now, but I can get the old regulator or the newer junkyard alternator to try them, but that doesn't seem to be the problem. Is there a magic resistance that'll work in place of the bulb above? A better circuit to try? I guess the next step is to check my library for a Pre-71 GM Chilton's with a wiring diagram, but I got the above hook up from 3 different sources (and it turns out it was what was on the tractor all along w/ terminal 4 being questionable)

Thanks in advance,

Bob Fourney

Put a diode in the problem wire. That will keep voltage from backfeeding from the alternator to the the ignition system.

Thanks all,

I think I understand. I was trying to avoid using a diode, mainly just because so many others have it working w/out a diode. Since this is a tractor, my "ignition switch" is a single position pull switch w/ only two lugs (one always hot, one switched). The diagrams I found made use of the "acc" position to stop it from backfeeding, a detail I wasn't initially aware of. I was also working under the assumption that it had worked at some point, but that's not certain (it has never worked for the current owner). I'll hunt down a sizeable diode and try that approach this weekend.

Thanks again,

Bob Fourney

Bob there is one other option. You can install a momentary ON push button switch on the dash between the 4 terminal and the ignition switch ON terminal. Aftre the engine

I think I understand. I was trying to avoid using a diode, mainly just because so many others have it working w/out a diode. Since this is a tractor, my "ignition switch" is a single position pull switch w/ only two lugs (one always hot, one switched). The diagrams I found made use of the "acc" position to stop it from backfeeding, a detail I wasn't initially aware of. I was also working under the assumption that it had worked at some point, but that's not certain (it has never worked for the current owner). I'll hunt down a sizeable diode and try that approach this weekend.

Thanks again,

Bob Fourney

Ignore this. I was thinking of an internally regualted GM alt and clicked the wrong button to delete, Ending up sending instead.

I think I understand. I was trying to avoid using a diode, mainly just because so many others have it working w/out a diode. Since this is a tractor, my "ignition switch" is a single position pull switch w/ only two lugs (one always hot, one switched). The diagrams I found made use of the "acc" position to stop it from backfeeding, a detail I wasn't initially aware of. I was also working under the assumption that it had worked at some point, but that's not certain (it has never worked for the current owner). I'll hunt down a sizeable diode and try that approach this weekend.

Thanks again,

Bob Fourney