Light Switch

Purchased a new 3 position switch( IHS 596) 12V for my 1942 Farmall A first checked the swithc with a ohm meter to check terminals and they showed headlight hot tail light hot and 4th terminal dead, Parts sent me a new switch and said to install per drawing with switch, did that and with the rear tail work light on the headlights are on but very dim when you switch on the head lights the rear work light stays on and head lights come on but there was a little smoke and the resistor coil glows red hot. This happens with both switches. What is wrong? Thanks

I don't think the switch cares if it is on a 6 or 12 volt battery. I did the same as you a month ago on my Super A, the new switch works fine, but I used all new wiring. Compare the instructions of your new switch with the diagrams in the operators manual and make sure it is wired right. I didn't think the diagram for the new switch was very easy to figure out -- maybe I got lucky.

The resistor should get hot, but not necessarily red. When new they do smoke at first.
The three positions are off, dim lights (through the resistor to the headlights only, full power to rear light)
Then full power to both front and rear lights.
This switch is designed for 12 volt operation with the low power bulbs that came with the tractor new.
If you use any after market lights at all, including brighter bulbs that happen to fit in the sockets, it will over heat the resistor. The method IH (and others) used to dim the lights was to put a resistor in the circuit. This was inexpensive and (In my opinion) worthless as the lights were so dim already that seeing was iffy at night. If you want to make bright light you will need to use 12v relays and connect the switch to relays to reduce the power through the switch. Also remove the resistor, and use a relay on the terminal for the resistor to power smaller lights, or double filament Halogen automotive lights. Short circuits to ground will also make the resistor smoke. Jim

Surely better to change to a voltage regulator. Saves heaps of hassle and reduces the chance of your tractor burning itself and your shed down.

Thank you Janicholson:
has been converted to an alternator and new wire harness, so you say to cut the resistor out of the switch if using new lights?
Would a 4 position switch allow head lights on and rear light off? and rear light on only?

New lights that draw the same current (Watts) as the old lights are no issue. The issue is that the resistor is designed to dim the single filament original lights. All voltage going to the lights when on Dim, as it comes from the factory, goes through that single resistor. If the lights are now drawing more power, the resister gets bright (too bright) and the lights get dimmer than usable.
The only way to use the original switch with more powerful lights is to use the switch to power a relay. 12volt relays have three terminals and a ground. one terminal is connected through a circuit breaker to the load side of the amp gauge.
the ground is grounded to the metal of the tractor. The control terminal is connected to the light switch terminal that is now connected directly to the front lights. The load terminal of the relay is connected to the new lights.
This allows the lights to draw more current without loading the OEM switch. The resistor is just not needed, I would take it out of the system by removing it from the switch all together. If you have a way to make dim lights (double filament bulbs, or automotive headlights),
a second relay could be attached as above except connecting its control terminal to the light switch where the dim resistor was attached.
The existing rear light will still work with full power at both dim and bright settings.
I hope this answers you question. Jim