How many wires do you need to run through the firewall, light gauge wire, amp power ect? If its just something like 4mm auto wire you can draw them through the rubber grommet with the main wiring harness on the drivers side. If its something thicker like an amp power wire you can either drill a new hole somewhere and put a rubber grommet in it or you can also run it back through with the bonnet release cable if you enlarge the hole in the existing grommet a little bit.
You might find a plastic grommet in the firewall on the left hand side near where the lefthand exhaust manifold is sitting in front of but the easiest way is to make one with a holesaw or punch...when they install factory cruise control at the dealers in the kit they give directions to put a hole between the wiring and throttle cable to the bottom to get the wiring through. http://forums.justcommodores.com.au...ns/27478d1159597195-vr-cruse-control-hole.jpg