'91 OBS wires to keep for LS swap?

[Tiger88]

Hey guys I'm wondering which wires to keep from my '91 obs chevy wiring harness during my 02 5.3/4l60e swap. I've read the altenator, coolant temp, oil pressure..any others?
How do I locate the exact ones I do not need in the old ECU? Is their a Diagram?

Thanks for your help.

[97greenbeast]

get a hold of silverado_lover, he may know

[Blasphemy]

All I can say, is that you've got a lot of thread reading to do and some note taking as well. I spent almost a year researching my swap and lurking all over the forums before I actually started and I've been wrenching my entire life, yet I still have questions unanswered. Your best bet is to gather as many diagrams as possible and start mentally planning what you want out of your swap, like A/C, stock gauges, ABS, etc. I went to the GM dealership and the guy was nice enough to let me pick and choose what diagrams I needed and even printed them out for me. It's best to keep the donor engine's harness as complete as possible so that you have little issue at startup.

[Tiger88]

So Blasphemy, did you figure it out? Is your swap complete?

[Tiger88]

So Blasphemy, did you figure out your swap? Is the swap complete?

[Blasphemy]

The swap is almost complete. I should be firing it up this weekend if all goes well. I forgot to mention that lt1swap.com is my bible when it comes to wiring tips, tricks, and diagrams. I'll be updating my thread "Just another LQ9 swap" when it's up and running.

[Tiger88]

Well my Ls wiring is complete. The computer is flashed. I'm just curious about the stock wires that connect to the new LS computer. Here is the info I have received from Brendan Patton from LT1swap.com:

"The 5.3l will have signals for check engine light, fuel pump relay control. You can tie those into the original wiring. You will want to use the original a/c wiring as well. You should also keep original speed sensor wiring in place, and tie the 5.3l speed sensor to the same wires already going to your speed sensor."

[88blazerboy]

One of these days, I'm going to unwrap my engine harness to map it out and get a good understanding of how it's built, but at this point all I can say is that I started with a full stock LMG wire harness (hooked up with all sensors in place). I learned what everything was, took pictures, labeled the pictures, and then took it off to pass on to someone else to build for my swap. What I got back had about 80% of the original harness in tact, and it went back together just fine. To make my Blazer's stock gauges work, I had to harvest a lot of my old 5.7 wire harness, but again, I let someone else do a good chunk of the wiring for me.

Wished I could help, but I'm pretty bad at electronics right now. Hope to be better by the end of this summer.

[1991SSP]

here's basically how I did mine on my 94 model 2wd that had a V6 in it originally


the wiring you need to worry about keeping is the AC, oil pressure and coolant temp wire, label all these as you unhook the stock harness from the engine. I left the entire stock harness in place until I had my swap completed. I then installed my LSX engine and transmission.. I used a harness from nelson performance as well... I mounted my computer under the hood and put my new harness on the engine and trans... I hooked up my ac wiring to my original compressor, hooked up my oil pressure and temp gauge wires. I ran the wire for the diagnostic port inside and mounted it where the original port was mounted. I ran the wire for the check engine light, speedometer, tach from the nelson harness into the cab thru the fire wall and connected them to the correct place in the original dash harness plug for my cluster... other than that you hook up the power and fuel pump wires for the aftermarket harness and you will be good to go... I do not have a show truck and was not worried about leaving the factory harness in the engine bay... As far as the rest of the original harness plugs that were not used I cut off the ends, put heatshrink on the ends of the wires and tucked them into the wiring loom to clean things up...

[Mickeymotormount]

I left most of my original wires in. Oil pressure, temperature, volts, A/C, speedometer and tach wires were all left and reused. Sensors were also reused with adapters to fit the LS block. Speedo and tach wires were fed directly to the new PCM. I left in the old PCM and wires and mounted my new PCM under the hood on the driver's side. I'm going on my 3rd year with 20,000+ miles without any incidents or problems.

Lots of research is needed as stated above. Brendan Patton's site was extremely helpful and he also flashed my PCM. I used the original harness and modified it to stand alone as Brendan indicated. It took about 2 months to complete but was well worth it.