90 sierra rcsb ls swap

[hotrod]

Hey everyone, about to do my ls swap, I just got a 5.3 motor and tranny complete from an 05 silverado last week at a good price.

I will be starting my wiring harness soon and had a couple of questions.

1. If i've been reading right the only thing I keep from the old harness would be oil pressure and water pressure and a/c?

2. Since my sierra has the moonie style gauges, how does the speedometer get wired in for the new harness to control the speedometer that's in my truck now?

3. The ses light, does the new harness get spliced in to the wire coming from the sierra pcm? I don't think I really found a definite answer on that from reading around online. Could someone explain how to use the ses light that's already in the dash?

One more thing, do I really need the oil pressure and water sensor adapter or can I get by without adapters using the sensors from my 350 tbi? Wrong size thread i'm guessing is why people use the adapters?

I will try to get as much pics as I can, hopefully some video too.

[hotrod]

forgot to add, this will be a standalone harness

[foreverfalcon40]

Congrats

I can not offer you any advice on the swap as I know shit about harness.

Please while the motor is out I recommend replacing all the gaskets.

[fordkiller91]

Go on PSI there harness starts at 499. I had mine set up with. 80e and ev6 injector pigtails. Almost 600 not to bad. The harness has wires ran so you can run to your factory gauges, but I don't the early 90's gauge so I'm going after market ones. You havd to have the factory cooliant gauge for the ecu. But on summit they sale the fitting kit for the coooliant and oil pressure gauge its like 50 bucks

[hotrod]

Go on PSI there harness starts at 499. I had mine set up with. 80e and ev6 injector pigtails. Almost 600 not to bad. The harness has wires ran so you can run to your factory gauges, but I don't the early 90's gauge so I'm going after market ones. You havd to have the factory cooliant gauge for the ecu. But on summit they sale the fitting kit for the coooliant and oil pressure gauge its like 50 bucks

thanks for the info fordkiller but I'm going to go ahead and do my own harness

[fordkiller91]

The true you don't use your serria wire harness if you get from psi. Pull Harness out from the fire wall on the passenger side its a bitch now get a heat gun n it be easier.unhook the four connection under. The dash where your serria pcm is and unbolt the thing that wired going through. And don't cut nothing. All you need alternator red wire battery starter wires and the fat pick wire that hooks to you factory coil.that's all I can think of right now if I can think of some else I let you know

[hotrod]

Here's pics of the motor and tranny. Got the harness removed also.

[fordkiller91]

Good luck..:|

[Chevy-Art]

1. If i've been reading right the only thing I keep from the old harness would be oil pressure and water pressure and a/c?

2. Since my sierra has the moonie style gauges, how does the speedometer get wired in for the new harness to control the speedometer that's in my truck now?

3. The ses light, does the new harness get spliced in to the wire coming from the sierra pcm? I don't think I really found a definite answer on that from reading around online. Could someone explain how to use the ses light that's already in the dash?

1. What you need from the old harness are the wires that go to you gauge cluster. They are oil pressure, and water temperature. For the water temp I drilled and tapped the water pump, probably not the best way but it worked for me. I think I used the LS1 sending unit for oil pressure.

2. For the speedometer to work I used the wires what come from the VSS on the transmission, they disconnect from the rear of the trans and go into the cab. The colors are HI 400 Yellow and LOW 401 Purple.

3. For the SES/CEL, you are going to have to tap it into the corresponding wire that comes from the donor vehicle PCM. And you are also going to need an ALDL/OBD II connector from a 96 or newer GM car or truck.

[hotrod]

1. What you need from the old harness are the wires that go to you gauge cluster. They are oil pressure, and water temperature. For the water temp I drilled and tapped the water pump, probably not the best way but it worked for me. I think I used the LS1 sending unit for oil pressure.

2. For the speedometer to work I used the wires what come from the VSS on the transmission, they disconnect from the rear of the trans and go into the cab. The colors are HI 400 Yellow and LOW 401 Purple.

3. For the SES/CEL, you are going to have to tap it into the corresponding wire that comes from the donor vehicle PCM. And you are also going to need an ALDL/OBD II connector from a 96 or newer GM car or truck.

Thanks man, that clears up the wiring i was wondering about.

You wouldn't happen to know what color wire the ses wire would be would you? Not sure if the wire colors vary from different years.