Electrical question

Rewiring my c after restoration and have no power to lights and amp gauge not showing it is charging.   I have power to both terminals on the gauge at all times. No power to the light terminal on switch when on or off . All other terminals have power. Why would the switch not be sending to the light terminal? Have a new switch from Steiner any info would help thanks.

If the ammeter isn't indicating it could be rusted fast or isn't wired right.

There should be two wires from the ungrounded battery terminal. One to the starter and one smaller one to the ammeter. Often the ammeter wire runs from the starter switch terminal to the ammeter. The other terminal on the ammeter has to be hooked to the B terminal of the voltage regulator or cutout. And that same terminal on the ammeter goes to the ignition switch (presuming not a magneto) and the light switch. Though the light switch could be connected to the L terminal on the voltage regulator when present. With the ammeter wired that way it sees all the battery current but the starter charging or discharging and the generator output can supply the light and ignition loads plus the battery charging. That's modern wiring.

The original C light switch supplies power to the lights and grounds the generator field for full or partial charging rate with a three brush generator and a simpler cutout. It leaves the control of battery charging to the operator and is prone to overcharging. It has to be wired right and I've read on this forum that many of the replacement switches except those sold by Steve (NJ) are not compatible with the battery box (which has to be grounded well for the generator field section to work).

I have a C shop manual on line with wiring diagram for B, C, CA, and G at:
http://www.geraldj.networkiowa.com/Trees/Allis-Chalmers-G-B-C-CA-Service.pdf 

Gerald J.



Edited by Gerald J. - 06 Dec 2016 at 6:31pm

the replacement switch has a bigger resistor on it. It will not fit in the B box correctly. You may have a pinched wire or grounded wire that is not suppose to be. Try with the cover loose and wires exposed out of the box.

With the engine not running there will be power only at the battery post of the cutout, nothing at the field or armature terminals on the generator or the A terminal of the cutout.

The switch gets its ground through the battery box and the mounting of the switch to the box, paint prevents that circuit at the switch mounting and the box mounting. There are two independent poles on the switch. One turns on the lights, the other grounds the field through the resistor or direct depending on the switch position.

Gerald J.

There is only two terminals that wiring can be attached to on the autolite generator I have.   One place being the voltage regulator/cutout other is a single terminal that I ran to the positive terminal on the ammeter.

The 2 terminals on the genny are marked A & F. A goes to the amp meter and F goes the the 3 position switch. As long as you get can identify the F terminal, the other terminal goes to the switch. Bob

The wire is coming to the battery/starter from the + terminal of the ammeter.  It should show a charge at that point.  If it does not it is bad.  The wire coming from genny to the - terminal also goes to the starter switch and the light switch.  If the lights don't work, it appears the genny is not putting out 12v, but you have 12v at the - term of the meter so the light switch is not grounded.

I think you have two problems!

got everything working today power to lights ammeter showing charging just waiting on the light reflectors to come in now to finish assembly.   When will I learn with these 6 volt systems grounding is crucial and can be any paint touching anything that is a ground.   Thanks for the help guys

Be very CAREFUL with that aftermarket 3 pos. switch. That thing does not fit correctly in most AC instrument boxes and shorts out! I had quite a few of our customer's fill me in on that switch because of that.  If you want the real OEM correct switch, we offer the switches outright if you don't have a core.