I finished my Harness the other day. I am making a direct Plug in Harness for a LSX Motor to directly go into my LT1 Car. I got all the wires traced out to go where they should go. I gutted the junk stuff out of the Harness(A/C, A.I.R., EGR, Cruise Control, Rear O2's, couple of other things) and got it down to the basics.
I traced the Data Connector wires so that I can tune it in the right places. 3 of the 4 wires there were already in place, and the 4th one that is not used by the LT1, which is used by the LS1, was in from the factory. I got this hooked up so I can tune it. Then I got the Starter wire to go in the right spot, and a few other wires moved around and hooked up. The LS1 Harness had a connection on the Wheel Well Plugs that had to be grounded, and the LT1 Car doesn't have this, so I made a Chassis ground out of one of the AC Signal wires that I am not using any more, and got that to plug in in the right spot.
I got it all to line up, it was not that hard to do, everything was right there. The only thing that I had extra was 2 wires on the LS1 Harness, one was for the Transmission(15A Fuse), and the other was for the MAF & O2's(20A Fuse). They are hot wires coming from the Fuse/Relay Box. I found an un-used Fuse circuit on the LT1 Car for this setup, and I am using that. I spliced both of them wires together, and I am dropping a 20A Fuse in that Circuit. Then I am putting an 15A Inline Fuse on the one that takes a 15A. I figure that should work. I also have to change a few Fuses in the Relay box cause they are a little higher in the LS1.
This is probably the hardest part, so once I get the Motor built, I will check it out and it should start. Everything is where it should be. If it works, I am going to do a write up on it. If anyone has any help or something that I need to do, feel free to chime in..

 

Beautiful!! I will be looking foward to your writeup. I have almost all the major components (engine,trans,stock harness, k-member, and trinkits) but I am concerned about the wiring. (mainly because I want it to appear stock) So your writeup will be of great interest. What year harness did you use? And what were your main resources for the wiring pin outs?
Thanks
Ken

 

I used a 1999 Harness, and got Pinout Diagrams from GM Alldata from a Dealership.

 

When I "pruned" my LT1 wiring harness down, I was amazed at the number of wires in there that went to things that had absolutely nothing to do with actually making the engine run. After all was said and done, there was a little over half of what was originally there left.

 

LT1 or LS1 Harness.. The LT1 is actually pretty basic, there isn't a whole lot there. The LS1 on the other hand, has all kinds of stuff in it that isn't really needed. I got rid of the A/C, A.I.R., Criuse Control(Car already has it), EGR, Rear O2's, Low Coolant and Oil Level Plugs, EVAP System, and all the Fuel Sensors except for the one labeled as 5v Refrence, cause that is the Fuel Pump/Sender Ground that goes to the Relay on the Drivers side in my Car. I got it down to pretty much everything lining up. There was 15 wires under the dash, and 7 or 8 of them on the Wheel Well. I spent a few hours on it.

 

I have a 2000 harness so that shouldn't be an issue but being that my car is a 94 the obd 1 under dash connector will probably need to be swaped out. You always hear of people doing swaps but nobody ever does a writeup so, looking foward!

 

Cool, you looked at that already. I looked at mine, and it is the OBDII. Then I traced the wires, and they were all in place for the LS1 Car. All I had to do was make them go to the right spots.

 

All things to be found in an LT1 harness. (Unless it's a 95-earlier which doesn't have rear O2's.)

I wasn't attempting to "one up" you with my comment, I was merely affirming the idea that alot of what's there can be eliminated.

 

I hear ya.. There is a few more things in the LS1 that aren't really needed. I am not disagreeing with you at all, both of these things have all kinds of **** in them..