So when you are taking apart the stock harness to keep the wiring that goes to the starter, the headlights, the fuel pump, etc, it all goes into a connector on the driver side firewall right? So do you keep that end of the connection, or do you cut off the wires you need to keep and leave the rest of the wiring intact, and connected to the connection? Does this question make sense? What I'm trying to say is, when you unplug the black connector at the firewall, there are tons or wires coming from the one end, do you cut off the wires you need to keep and splice them into the LS1 harness, or do you cut off the wires you DON'T need and keep the connector in tact with the brakes, headlights, fuel relay, starter wires? I have a feeling this question is a little confusing, but someone has to know what I'm talking about. I'm trying to take apart the old wiring this weekend and without ever having done this before, I want to know which way you go about it.

the C100 connector on the firewall will seperate to 2 different harnesses once u remove the 1/4" bolt.
1. engine and gauge harness
2. headlight, fan , horn etc harness.

u wouldnt touch harness # 2.

All the splicing to the LS1 harness would be done at 1.

#1 also connects to the passenger side harness for ecm power etc

You have no reason to open up the light harness. Leave it alone

Next Ill stand on my soapbox for a bit and try to save you a bit of money
Dont cut up your TPI harness, sell it
Get a similar year V6 harness from a JY

You will be removing everything ECM related, which is everything that makes it a V6 or TPI

Now, take the 3rd gen engine harness and label each connector
Decide if it ran the old engine or if it controls a gauge. In a nutshell, if it goes to the ECM its getting removed

Once all the connectors are labeled and you've decided the keepers and the tossers, strip all the loom off and cut the unneeded wires off

You should be left with this:


You are left with the power wires running to the starter(can be moved off the starter), purple starter wire, IGN/tach, gauges, relay leads if you are moving them or using LS1 relays otherwise the relays stay put with the old ECM engage wires intact and SIR grounds(if retained)

I actually did sell this harness. The buyer knows I am cutting out some things and he is ok with it because he is putting it in an old full size truck. He'll have to make up some different wiring anyways.

What pocket has there looks to be exactly what I wound up with. THAT is the way to do it in my opinion. Make it nice and neat, cut what you dont need, route and re-wrap what you do need.

Thats a really good pic Pocket...good example of what that plug should look like when done.

J.

Agreed. Cut neatly at the plug the wires no longer needed. I have no splicing that takes place at the actual brake booster C100 connection. As you see in Pockets pic it leaves enough wire to run out to where the splicing needs to be. In fact there is no "splicing spot" on my harness there all splices all throughout. I ran the wires as neat and as far as I could and most of them made it to where they needed to go and I spliced there. Unfortunately a couple of leads needed to be lengthened... One of them was only about two inches in my case but I suppose I should have just used my wire stretcher and all would have been well

Crap not that I got a good look at that picture, I don't think the harness would be usable after I'm done cutting out the stuff I don't need. I think I'll take Pocket's advice and buy another harness from a salvage yard so I don't give my buyer a heck of a time with wiring up his truck swap.

Does anyone have a picture similar to what Pocket posted for the C207 connector? That would be AWESOME if someone had one.

C207...that's the one under the passenger side dash correct? You'll need several from that. Mine had the fuel pump wire, MIL, PNP, brake switch, and maybe a couple more. I went page by page in my Helms looking up each wire in that thing for mine...but as yours is 4 years newer I'm hesitant to say they'll be the same.

Question....you said harness #1 is for the gauges. Does that mean that if I run a wire from this harness on pin "blah"..."I don't know the location right now". To my oil pressure sending unit and a wire from pin "blah". To my water temp sensor it will work?

I bought a 88 GTA someone did a carb swap on and the wire harness is all hacked up.

The C100 is the factory 3rd gen engine harness bulkhead connector. Most of the gauges run thru it

Both #1 and #2 are C100, it is split into halves. Engine side and light side

If your harness is beyond repair, get a new one. V6 should work since a carb uses nothing TPI or V6 You will either keep the ECM inplace or retrofit a buffer box in to drive the speedo. Older models like that may already have the buffer box, Im not sure