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Farmall A cut out relay wiring

B

brooktre

Member
I have a 46 Farmall A and have a question on wiring.

Current set up:
1- has a 6 volt positive ground
2- has a 4-position switch (although the label is O-D-B)
3- there is a wire from the switch field resistor terminal to the F terminal on the generator

Reviewing various wiring diagrams, this looks good and the tractor is charging and operating normally.

However, there is also a wire connecting the F terminal on the generator to the F terminal on the cut out relay. I have not seen this connection on any of the diagrams that I could find.

What does connecting F to F do and should I leave it or remove it?

Thanks for any help!
 
Great question. The tractor could be purchased with no lights. In fact it had to be ordered with lights unless bought off the lot with that option on
it. With no lights, the generator was set to a small maintenance charge by running a wire to a resistor under the cutout. This fixed resistor is just
grounded on the frame of the cutout, and is not a part of the cutout action. That wire should not be connected if you have a light switch with the 4
positions. With it removed, the L position on the switch will provide a minimum charge. When starting and stopping the engine often, prudent use of
the H position will assist in keeping the battery up. Jim
 
To back up what Jim said, here's a factory drawing showing the "F" terminal on the cutout (Key #29) unused with the lighting equipment installed, and the generator's "F" terminal (Key #27) connected to a wire in the harness that passes back to the light switch.

<img src = "http://oi68.tinypic.com/2ypb611.jpg">
 
I've seen some that weren't stamped very well. But both terminals will be stamped. Usually at least one is stamped clearly enough to be read without question. If you can read one, you can figure out the other!
 
Thank you for the responses. I couldn't see any letters on the generator, but I didn't look too hard. Other than the F to F wire, everything was wired properly. I only looked at the wiring because some of it needed to re-insulated and I was changing the battery. The one I replaced lasted 13 years so I didn't suspect that anything was amiss. I also did some research on the wiring and found that I had the 4-position switch. I never understood why there were 4 positions when the label on the tractor was O-D-B. And I didn't know how the switch worked because when I got the tractor there was no internet and my shop manual didn't cover lighting. I rarely use the lights.

I'll remove the F to F wire and take some before and after measurements.
 
I removed the F to F wire. I also found the F stamp on the generator and it is properly connected.

I took measurements before and after and they were virtually the same with and without having the additional jumper wire F to F..

Readings at idle - switch position ():
(L) 6.3 volts / 1 amp
(H) 8.2 volts / 10 amps
(D) 6.5 volts / 0 amps
(B) 6.4 volts / &lt;0 amps

Readings at full speed - switch position ():
(L) 7.8 volts / 6 amps
(H) 8.2 volts / 12 amps
(D) 6.5 volts / 1 amps
(B) 6.4 volts / 0 amps

I'm not sure how these compare to "good" readings. The 3 lights (2 front + 1 rear) seem to pull a lot of power! In any case, I rarely use them and since my last battery lasted 13 years it must be OK.
 
The resistor in the cutout might be broken. It is about 3 ohms or so and would make a difference. Jim
 
If the field resistor on the light switch is broken, the generator F to cut-out F jumper would substitute the one on the cut-out in and the system would work as designed. If the resistor is broken without the jumper, the "L" position wouldn't produce any charge.

I'd say the posted measurements look pretty good.
 
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