Hi There:
I have been reading about wiring when swapping a LS engine into third gen on this forum and I have some questions if you don't mind me asking.
I really don't have any electrical/wiring background 9I just follow the diagrams and so forth) but I have modified the LS wiring twice before when I did 5.3 vortec swap in my 79 Camaro and 72 Nova. The stand alone LS wiring harness with its own ECU just need the feed from the IGN and 12 V ACC to function and run the engine and fuel pump so, can I just leave the existing wiring in 92 Camaro alone and just use an IGN and 12 v ACC feed from it? Is it related to PCM? This is my first third gen and I even don't know what exactly the PCM does in this cars since I bought the car without an engine. I know it would look cleaner to take everything apart and re-mate the two harnesses but if there any other specific reason the stock third gen wiring has to be taken apart? I know the tach signal has to be addressed somehow and also, the AC system which I don't plan to use anyway for now, it is a convertible car in WA!

 

Read the LS1 harness stickies to get more familiar. You will need to tap into OEM wires for your gages to work. It is true many wires won't be reused but I would spend some time and carefully read through this.

https://www.thirdgen.org/forums/ltx-...p-3rd-gen.html

 

Yes, especially under the hood A LOT of wiring is no longer needed.
Not so much for the lighting harness, but the ECM/engine bay harness cleans up quite a lot ! I'd say it's worth it.

As inspiration, I've attached a picture of my 1988 ECM engine bay wiring. Upper left is what to keep. Upper right is what goes away (I've cut about 4 wires).
Lower is a part of the HVAC wiring, which I will keep and install later when the LS engine is in.

 

Where in Washington do you live? I’m in NW Washington (see signature). I may be able to help you out if you’re close. You can PM me through this forum if you’re interested.

 

Thank you guys.
I have been reading the wiring modification sections on this forum. I was just trying to avoid extra work since I am doing two different projects at the same time.
soloc4, we are very close. I am in Snohomish. I may take you up on your offer. We'll see how it does.
Happy holidays and cheers,

 

Okay, I am a little confused after all these readings, please forgive my ignorance. What does the third gen ECU controls? Just the engine performance? Or does it sends signals to gauges and everything else like more modern ECUs? I see the light harness is separate in engine bay but it seems the heater/AC goes through the stock ECU as well.
Since the LS engine comes with stand alone wiring harness and ECU (I modified my LS wiring harness based on lt1 swap website), there won't be any need for the stock ECU any more if it just controls the engine?
Thanks

 

You will not need the stock ECU anymore and the LS ECU you can think about it generally as a stand alone, ie it is controlling the engine and your interface with it will be minimal in regards to other functions. However there will be some basic inputs and outputs that you will interface with besides providing it power, ground, and all its direct engine connections. As examples you will get your tach signal and mil signal from the ECU. The ECU also can and generally does control your fans.

if you look at post 150 and several others around this area of my LS3 swap thread it will give you a good idea of what needs to be done
https://www.thirdgen.org/forums/ltx-...ne-swap-3.html

 

It also controls the lock-up of a TH700, but nothing else on the transmission. And it controls the cooling fans.

No, and no. Actually, the speed sensor is an input on the ECU. Also the A/C request is an input. The entire heater/AC system is standalone, the input to the ECU is used to bump up the idle speed a bit.

No, there is no need. If you keep a TH700, you'll need to control the lock-up some other way. Same goes for the cooling fans. Easiest to do is to use the LS ECU for that.

 

Thank you guys for clarifications. It helps a lot.