Originally Posted by DerTruck

Because of the melting headlight switches on older models the headlights on 99+ are "ground switched". The pin on the bulb that is typically used for ground is powered directly from the PDC and the headlight/hi beam switches connect either filament to ground. Incandescent light bulbs don't care which way the current flows but aftermarket LED/HID do so that is one thing to consider. In stock form with the lights off you will measure battery power on all three headlight pins, that is because one pin gets power (see above) and the other two are just dangling unconnected. The filaments are very low resistance and a voltmeter places no load on a circuit so it just reads 12V on the other side of the filaments. Switching on either filament connects that side to ground (no voltage reading) but the other filament is still unconnected and still reads 12V.

Edit: I think I know where the confusion is coming from. What I wrote above is correct but the high beam indicator in the dash works the same way. Even with the headlight bulbs removed there will be 12V on the high beam side with high beams off just getting there a different way through the dash indicator light.

Originally Posted by Moparite

Why are you tapping the wires from the switch? You can tap off the wires at the headlight plug. Regardless of what is switched you can wire relays in there.

Originally Posted by quadrunnerjake

1- RD/OR - high beam wire to dimmer switch, then to ground