lt1
 

I'm going to do a swap is it better to buy harness or use car harness .I have a whole donor car.the LT will be going onto a 79 malibu

I tried to cut and splice the old harnes while swaping an LT1 into my 67 camaro. After three weeks with schematics, spliced wires, and tired eyes; i came up with just enough reach in the harnes to make it to the fire wall, but not through to the other side.
I ended up buying a harnness with 3ft extra reach which put the computer under the back seat. Worked great.
Save your time and buy a predone harness.
m.02c:lateral:

My harness came from Street and Preformance. Real nice harness.
PS i know my spelling sucks, bear with me.

Must have gone to Shumway..... :rofl:

Seeing as the OP is from 2 months ago this might not matter, but actually you can use an OE harness and get the PCM under the dash. It just depends on the donor car (where the PCM was originally located) and where you want to run the harness through the firewall. If the donor car is an F-body, the harness has more than enough length to put the PCM under the dash if you run it through the firewall around the middle of the car. While I didn't put mine under the dash, the harness easily had 3-4 inches of extra length in the harness that I had to bundle up and tuck into the opening between the fender well and the firewall.

If you're like me and need to keep expenses down, using the OE harness is the way to go. If you've got money budgeted for an aftermarket harness go that route. As has been posted here many times, it's all according to how much money you want to spend vs. how much work you want to do yourself.