Farmall H headlight switch

I have a 4 position switch for my H I was just wondering if anyone knows what the D position is? I have L H D R, I understand the L -low H - high and R - rear light but what is D? Someone took out the original switch and put in a toggle switch. I found an old H setting in a field and the owner sold me the switch for 5 dollars. All I had to do was battle the wasps that had a nest in the switch and amp gauge box.

D is for dim lite if you have the sw wired such. If your Gen has a reg you wont need the HI-CHARGE position nor the wire from the gens field to the sw. That wire was used on the early three brush gens along with that 4 pos sw. Later when gen was changed using a reg the sw only had 3 positions. What is the Delce-Remy# on your gen as that will determine which reg you will use as there are two regs for an H

I had thought it was B instead of R and stood for bright, but I could be wrong.
Zach

The L is for low charge through a resistor on the switch (using the light switch as a combination charge rate control, and a light switch), lights off. H is for High Charge direct field to ground through the switch body and elect box, lights off. D is for Dim lights through a wire wound resistor on the switch, and high charge. B is for Bright lights, no resistor and high charge.
John T analysis

My diagram

wiring diagram

Additional comment: If you wire a 4 position (LHDB) switch onto a tractor with a voltage regulator, the L and H positions do nothing except become two alternate "off" positions for the lights.

Up to about 1949 or 1950, on the H you could get two types of lighting systems. One was the "no battery" Bosch system, and the other was the Delco-Remy system. The Delco system used a generator, battery, the associated wiring, and two front lights with one rear.

Some time in '50, the H used the newer Delco system, but this one had full voltage and current regulation. The older system had a voltage cut-out and a third brush in the generator. The easiest way to tell the difference between the two systems, was by the light switch and the regulator. In the later system, the regulator was located on the rear fuel tank support, directly behind the steering post, and the light switch only had three positions.

The older Delco system had the "regulator" (this was the cut-out) mounted on the top of the generator. Both the old cut-out, and the newer regulator looked the same, but were electrically different. The switch on the older system had four positions as follows from extreme counter-clockwise to extreme clockwise: L(ow), H(igh), D(im), and B(right). A previous poster outlined those functions.

To double check the system you have, and verify the type, just look at the generator part number and check that with the parts book. If your tractor is a '48 or earlier, it is a pretty safe bet you have the older system.

A disclaimer here on identification: I have heard that a few of the early regulated systems had the regulator installed on the top of the generator as was done in the old system. In such a case, you definitely need to check the part number on the gen. to verify the type.

As a short cut, you can also remove the band on the back of the gen. and simply count the brushes inside. The new generators only had two brushes, while the older ones had three.

Our 41 H it was L, H, D, & B and I think you are confusing the B with a R as there was no R. The lights were all hooked to same way with the D being dim that you could hardly see them burning if you looked straight at them and was totally useless for anything. B was the only posisition ever used with lights and the Low charge setting was never used either, never overcharged while out plowing or disking all day. Usually was not run at night. Had that tractor from 1949 to 1983.