[davepl]

Turns out mine was not suited for out truck. My approach of shorting itself out actually does work, though. But with an external wire you need something like 2 gauge and a heavy rated resistor.

Which, it turns out, is exactly what's inside the one I finally got that works. There's a heavy rod with a resistor inline that does exactly what my approach above does, but because it's internal and integral they don't have to worry about wire gauge and wires heating up and so on.

Moral of the story: don't spend a week working on a part that you don't know to be functional in the first place!