Herb

Is it nessesary to pull the engine to replace the engine wire harness?

WVZR-1

Much depends on what's considered the "engine harness" Look at the FSM for C100 "pin-out" - that's the considered "engine harness". Does that encompass everything that you're concerned with? FSM @ about 8A-202-13

Herb

It appears that there is some shorts between where the opti connects to the harness and the computer.

WVZR-1

Never owned an LT1 but there's a short harness opti to the harness that I believe is an often failed part. You've confirmed it's OK and function?

A GOOGLE search 12106559 might get you a visual.

Herb

It's not that. It's between that harness connection and the ECU.

WVZR-1

There's only 4 wires. Have you confirmed at what pin on the ECM/ECU that you have issues? I'd think (pure speculation) that there's absolutely no need for you to even consider a engine harness replacement. Try maybe some of the FSM diagnostics. The 4 circuits should be in the 6E3-A-9 and many other places. When you had the engine out recently did you have any of the ECM/ECU connections undone? I'd start there and maybe mention what your issues are. Any codes or maybe run characteristics that you're experiencing.