I'm trying to decide how to wire my rear window defrost in a wagon that didn't originally have it. I've got a rear gate with the grid installed, and I've installed an original two position pull switch on the dash.

I've encountered a few interesting things. The resistance across the rear grid is about 2 Ohms. Seems a little high to me. With no other resistance, that would only allow 6 amps and 72 watts. The switch operation is also strange. It has 3 terminals, a + terminal, and a 1 and 2 terminal. All terminals are open when the switch is closed. In position one, the + and 1 terminal are closed with 0.2 Ohms and + and 2 are open. In switch position two, + and 1 are closed but with about 30 Ohms, and + and 2 are closed with 0.2 Ohms.

I've read that the defrost had two power settings, low at 40 watts, and high at 150 watts. I've also heard that 12 V to the + terminal comes directly from the fuse box, without any relays.

The question is, if both terminals 1 and 2 on the switch are wired to the grid, how does this low and high setting work? It seems like both switch positions would all the same amount of current to flow, and that current would be far lower than 150 watts.