I'm also pretty sure, the wiring in the later model trucks is wired alittle differently than older turcks, meaning, they don't ground the lighting fixtures directly to the body at that location of the light, it runs through the harness somehow or another.
I tried adding some side lights to my truck by patching into the front marker/turn signal lights, there were only two wires, i assumed one was hot, one was neg, i was wrong...
during one operation of the lights, if i grounded the add-on light to the body,then the other wire to one of the two feeding the front turn signals, one wire would light on while the parking lights are on constantly, or by switching the wire to the other, it would flash with the front turn signal, but not stay on otherwise..
I really haven't dealt with the wiring much more to figure out how everything is wired on these trucks, just thought that was weird.
and if you're thinking this was in fact a 3 wire deal, and was grounded at the light, i patched into the small (194) bulb wiring of the front fender side light, which does stay on constantly while all lights are on, but flashes when the turn signal is on. So again, it's weird to me currently how they are wired.