Engine Swap wiring questtion
 

I'm beginning my LFX swap into my 2002 NB. Drivetrain is out, dash out, and I'm sorting which wiring I will keep, and what can be eliminated. I expected the engine loom would be a contained, separate bundle, straight to the PCM, but it splits off into a large group that has a blue harness junction clipped to the heater core housing, just right of the steering column. (photo, with star drawn on). My question is whether this can be unplugged, allowing me to keep the engine harness whole, and pull it from the car, or do I need to track each circuit, and potentially keep a bunch of it. I will be using the stand alone V8R LFX harness, which makes sense to me, but want to avoid stupid mistakes with the existing wiring, as I eliminate unnecessary runs. I know you swap guy's have run thru this, so hoping someone can guide me! Thanks!

I can't speak authoritatively for the NB, but I can confirm the NA there is not a separate harness for the engine. Injectors, coils are in the same harness as headlights and turn signals. I had to decide which wires I needed to keep and then depin the rest.

Everything in this blue junction leads to one of the 3 PCM pin outs, and as I'm removing the stock PCM, I'd hoped it all could be deleted; wishful thinking I guess. As a red/green color blind guy, I'm not in my element fishing thru the maze! Thanks 'tho, and also for your great LFX blog! Tom

It can *mostly* be eliminated. There are a few gotcha's / wires you need to retain - keep in mind, since I did our harness I'm not aware of the specifics of the V8R harness - and this is all on our NA.

A/C wires need to be retained - again, on the NA - there's 2 inputs and 2 outputs. These need to be connected together so you can control A/C fan(s) and copressor. The stock ECM passes through the signal except when you're at WOT or high RPM.
Coil Power Wire - I used this for powering the main powertrain relay in the LFX's fusebox. It's one of the few signals on IG1 (when you key to the "start" position, IG2 is disconnected to provide maximum power for the starter and things that make the engine run).
MIL lamp - leave this so you can repurpose it to the GM ecm, works exactly the same.
Fan Relay Control Wires - again, this is probably completely different with how V8R does.

That's.. really about all I can think of for the moment. There are inputs on the LFX ecm for connecting brakes and clutch, and it was one of those "Eventually I'll get around to it" things that I never got around to. Doesn't appear to effect performance though.

Almost forgot - Fuel Pump Relay control as well.

Thanks, very helpful. The V8R harness will run the engine with only 5-6 leads completed; basic 12V, starter button, etc. and the LFX PCM will control both fan relay's. I will track down the circuits you have listed, thanks for simplifying it!

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