[MrBB]

On my car I ran a power wire through the hole in the firewall where the underdash harness exits to the engine compartment. I simply took a sharp knife and made a small hole in the rubber boot that seals around the harness in the firewall. I made the hole only large enough for the wire to slip through but still have a good seal around the wire. (an extra hand to hold a flashlight never hurts) So far it works great for me. Hope this helps! And good luck!