[joedoh]

I used a factory s10 harness pass through, it is rubber and pulls tight to the firewall with three bolts. you just cut the same hole in the firewall as the s10 has and bolt it up. It has some goop on the wires to seal it completely, but if you look around in a salvage I bet you can find one similar on most GM and just chop the harness and take the pass through.