Ok doing a LT1 swap would it be better to leave the 305 harness in and splice into it. Or just pull it out and put the one out of the LT1?

 

well, the way i did it was by pulling the harness through the extra hole in the firewall and splicing underneath the dash. I pulled the LT1 bulkhead, and LT1 connectors through...connectors C210,C220,C230. I did it this way because of all the underdash wiring harness from the LT1 like the program port, VATS, fuel pump relay. I think I'm going to rewire it so that I don't use the LT1 bulkhead but rather splice in the wires from the LT1 bulkhead to the thirdgen bulkhead at the firewall side. Because all i'm using off of the LT1 bulkhead is the power wires.

The headlights and stuff like that work off of the thirgen bulkhead wiring. However you wire it, to be safe, cut the wires you won't be using after you get the LT1 running.