Farmall Generator wiring

I have a 1940 farmall and trying to figure out if
I have something missing to wire up my generator.
I have checked the wiring diagrams for generator
wiring and everything is hooked up except for the
wire that comes from the generator and goes to the
light switch. There is usually a resistor located
in the light switch. Problem is I have no lights
or light switch on my tractor. I notice on some
pics it appears the light switch is on the ammeter
housing. On mine the kill switch is on the
ammeter housing and I have no other "box" or
switch. Am I missing something or being this is a
1940 was it just wired differently? Does this
wire just need to go to the a wire wound resistor
to ground? I guess I have a "cut out style"
generator as it has a box mounted on the side of
the generator

On a farmall with no original lights, the cutout relay had (or has) a third terminal. this is labeled F. it connects to the Field terminal on the gen. It is a fixed wire wound resistor directly to ground. This system allows the generator to charge enough to keep the battery charged but that is all. It does not change the charge rate. With a Magneto, and with no lights the charge rate is usually about 7 volts. Maybe a little less. If your cutout has no third terminal it is the wrong one. If your tractor has a voltage regulator it would be attached in a similar manor to the 3 terminal cutout. It might have a 4th terminal which would be an L terminal standing for load. (it would poewer the lights and ignition (if it had a points and coil type ignition.) Jim

A big "Ditto" to Jims instructions. Now to your question " Does this wire just need to go to the a wire wound resistor to ground?"

If theres no (as normal) F terminal as on an old original Cutout Relay,,,,,,, And you dont have a full fledged 3 or 4 terminal Voltage Regulator with the F terminal,,,,,,,,And theres no LHDB light switch to wire to the gennys FLD post,,,,,YES a wire from the Gennys FLD post attached to frame ground via say around a 3 ohm series power resistor will allow the genny to charge. The less resistanee the higher the charge, but if its too small (like a dead ground) the battery could theoretically overcharge if you ran for hours not using any lights and had a good strong genny. If you go buy power resistors Id try say a 2 and 3 and 4 ohm and use the one (or combinations) that made her charge maybe 5 to 10 amps at fast RPM, although 10 amps for hours at a time with no lights may be too much???


YOU SAY

I guess I have a "cut out style"
generator as it has a box mounted on the side of
the generator.

I SAY

If it has ONLY 2 terminals, BAT and GEN/ARM yes its a Cutout Relay

If it has 3 terminals BAT GEN/ARM and F and only has one internal coil and a wirewound resistior in the F circuit to ground,,Its an original Cutout Relay (wire gennys FLD to F)

If it has 3 terminals (BAT GEN FLD) and 2 internal coils its a Voltage Regulator (wire FLD to F)

There,,,,with this and Jims post you should be able to figure her out

John T

Sorry for the confusion. I was confused on the terminology. Yes it does have an f terminal. Where was the wire wound resistor from the factory? In the kill switch ammeter box? So if i put lights on the tractor layer ill need the switch to change f terminal resistance so it will make up for the load of lights and still charge

Where was the wire wound resistor from the factory?

If it has the Cutout Relay (1 coil, BAT GEN and F, designed for non light tractors) the wirewound resistor is inside the relay box....

If it has the LHDB light switch, the wirewound resistor is on the back of the switch (the other coil of wire resistor is light dimming)

So if i put lights on the tractor layer ill need the switch to change f terminal resistance so it will make up for the load of lights and still charge

YES if you use lights and install a LHDB light (Gennys FLD post wires to it) switch it adjusts for Low (L) (grounded via resistor) or High (H)(dead ground the Field) charge subject to which setting you desire...If you simply toggle switch the lights on your own, you can use a double pole switch so when lights are on the field is dead grounded (High charge) but when off the ground is via the power resistor I described below (Low charge).

Maybe Jim or Bob M can verify this, theyre better on IHC then yours truly.....

John T

I have my B set up with a diode instead of a cut-out. It has a 3 brush generator . I grounded the field then adjusted the 3rd brush for about 7 or 8 amps. It is enough to keep the battery charged without boiling the water out. It is run on short trips & not hour after hour in the field. Works fine for me. Tractor has a mag.

Ok so I think I have the generator with cutout relay on it. Everything was wired up except the f terminal wire is going to the front BY the ammeter and kill switch box and dangling there. So was this just running to a switch which should be grounded since the resistor should be in the relay box mounted on the generator? And if there is a switch is the purpose to turn the charging off to the battery manually? Or does it just stay grounded somewhere?

A switch to ground at the operators station (where is your choice) would allow the F terminal to be direct grounded giving full field output to charge a run down battery. (that is what the light switch does on H D or B positions.
A tractor with no lights could still use one to help recharge a battery or for short term winter use. Connect it to the F terminal on the Cutout allong with the other wire going to the Gen Field terminal.
Switch off low charge through the resistor in the cutout box.
Switch on full charge. Jim

...... Where was the wire wound resistor from the factory? In the kill switch ammeter box?....

Click to expand...

t was mounted on the light switch. With no lights it uses a resister built into the cutout box mounted on the generator.