I am having the same issue. After reading another forum I looked at a wire harness under the front passenger kick board and found burnt wires. I spliced around the harness and still have no power to the defogger. It appears to me that GM has massively undersized the wiring to the defogger and I plan to run a jumper wire around all the harnesses straight from the fuse panel under the hood. It is a solid wire behind the harness at the kick panel. So I only plan to go that far. If you run your jumper from the relay controlling the defogger it should all work properly and only cost about $5 to fix.
P.S. The fuse that runs it is battery fuse 3 right next to the relay.
Friday, January 7th, 2011 AT 10:26 PM