Well I think I know the problem...
Tore the headlights off and started testing voltages, using the working passenger assembly as a reference. The DS HB is only getting 5 volts in HB mode. For some reason, it isn't even illuminating partially (as it would in DRL mode).
The harness runs from DS headlights underneath to fog lamps and motor fans, and then back to PS headlamps and into the front relay / fuse box.
I ge tthe full 12 volts across the connection at the fuse box, so wiring to switch is assumed OK (correct me if I am wrong).
My best guess is that the wire is fried somewhere in the harness and is shorting.
SO, any guesses as how to find out where it is fried without troubleshooting the entire harness? Harness runs $300 from GM, and I'm not replacing it.
Last edited by Rusgreim; 07-31-2008 at 11:58 AM.