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Farmall H light switch


d_loeff

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Does anyone have a way to test the light switch on an H? I'm not sure of the proper way to test each position and what the ohm meter should read. I'm also looking for a wiring diagram for it.

Thanks, Darin

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Not sure about the "H" but all light switches should be the same. A light switch is a simple off and on so it should have continuity or not. If it is connected to dome and dash lights the switch will be more complex.

Hope this helps.

Luck

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No, it's not that simple. There are three different positions I believe, off, dim, and bright.

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...and it depends if you have a magneto or a distributor. A 6V magneto with a simple cutout has a 4 position switch: low charge, high charge, dim beam and high beam.

What year and setup do you have?

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If you have the three position switch you will not have the fuse on the back side of the switch but rather they use a separate fuse assembly.

(O) In the off position there should not be continuity between the battery lead terminal and any other terminal.

(D) In the dim position there should be continuity between the battery terminal and the rear light terminal ans also the terminal where the resistor is connected opposite the terminal where the head lights are connected. You will need to remove the connection from one end of the resistor to test which terminal gets power since with the resistor connected and no load on the circuit both terminals will show the same voltage.

(B] In the bright position there should be continuity between the battery terminal, the rear light light terminal, and the head light terminal.

It has been a long time since I checked out a switch like that. I don't remember if the dim terminal side of the resistor has power to it in the bright position or not. It doesn't need to but it wouldn't cause any problems if it did. I don't remember what the resistance should be across the head light resistor but if it has continuity from one end to the other most likely it is good.

If you have the four position switch the lighting part of the switch is the same with the exception of the fuse being included on the switch rather than remotely mounted. Both the (H) high charge and (L) low charge positions are Off positions for the lighting circuits.

Both of the diagrams above are incorrect in regards to the connections of the charging circuit resister. Both ends of the resister are connected to the switch. When controlling the charging circuit the switch works by grounding either end of the resister to ground. When the end of the resister that has the wire coming from the F terminal of the generator is grounded through the switch, the generator will have maximum output. If the other end of the resistor is grounded instead the output of the generator will be reduced because the resistor cuts down on the generator field voltage.

The L and H positions of the switch deal with controlling the output of the generator. This system does not use a voltage regulator but rather only current relay connect the generator output to the battery. The generator output is controlled by the L and H positions of the light switch. To test this part of the switch disconnect one end of the resister and check for continuity between the switch housing and each terminal. The H and L positions should have continuity to only one terminal for each position. In the L position the end opposite where the wire from the generator is connected should have continuity to the switch housing. In the H, D, and B positions the terminal where the generator lead id connected should have the ground continuity.

PS. I learned something new while posting this. If you type a capital B with parentheses on either side you get this: ( B).

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