Farmall M--4 Position Light Switch?

Tue May 03, 2005 11:17 pm

I have to wait a few days for some Cub parts so decided to get the old M tractor moving. Rebuilt generator, starter, new homemade (temporary) wiring harness. New Rochester Amp. Gauge and new starter button. Cleaned battery connection. Put on a new Optima 6 volt---started right up on first try. Now the problem.

The decal on the gauge box says ODB (3 position) but from the OFF I get 123 clicks--makes it a 4 positon switch. Followed Robert Melville's wiring diagram so I believe it is wired right. Amp gauge showed no movement or very little in either the first or second position. So I followed an earlier posting a jump wired from generator F to the cutout mount screw. Amp gauge showed charge 6 volts more or less. I haven't ran the wires from the switch to the lights yet but don't believe this would have made a difference.

First---Is this a 4 position switch as I understand it to be or am I in left field and if it is why would it not register charging on the amp gauge until I grounded the gen. F field to the cutout mount which I understand creates a high charge rate. Sorry the posting is so long.

Wed May 04, 2005 9:18 am

Gene, It is a 4 position switch. In the first (L) position the switch should ground the field terminal through a resistor. In the second (H) position, it should ground the field directly. This is apparently not happening. I would check the ground connections closely.


Wed May 04, 2005 9:25 am

Thanks BD
I was searching old posts and was coming to that conclusion myself especially since when I ground the gen F to the cutout mount screw I show a good high charge on the amp gauge. I am going to take the light switch off and clean all connections and the control box it is mounted in. It looks like a good switch but just isn't working right now.l