ls swap into 78 chevy question

**isabellsdad** · 02-08-2015, 08:23 PM

Hello I am from Tucson az and am swapping a 4.8 from a 05 Chevy Silverado to a 78 c10. I want to retain as much of the factory harness and ecu from the 05. What wires can I cut and still be OK? I mean the wires going into the cab on the driver side firewall. Obd2 and whatnot. Thanks in advance

**JustinEntropyRad** · 02-09-2015, 08:36 AM

If you dig around on here and LT1.com there are a few good threads on DIY harness work!

**isabellsdad** · 02-09-2015, 08:40 AM

I found one but it was only for modifying the harness and I don't want to modify it in any way.

**pajeff02** · 02-10-2015, 03:11 AM

You should invest in a factory service manual or get your hands on the wiring schematics. It is about the only way to know what is going on. I never really looked at the wiring on our truck, so not certain what is plumbed on that side of the firewall.

**Firebirdjones** · 02-10-2015, 04:01 AM

If you are trying to use the factory harness from the 05 truck, you'll definately be modifying it extensively to fit the 78. There is a ton of stuff you just won't use, depending on where you mount the computer, etc....you'll be removing alot of that harness, alot of soldering, and remaking some sections. Pinning the computer to find whats what, you'll need wiring schematics. No way around modifying it that I've found when using OEM harnesses.

Anymore the best solution rather than dealing with 10-15 year old wiring and spending dozens of hours to do it,,,, is to just have a complete plug and play custom harness made. Tell them the vehicle and where the computer will be mounted and it's made to fit, all brand new stuff that isn't brittle, with correct GM weatherpacks. I use Howell for this service but if you want to stay local and since you're in Tuscon you can try Arizona Speed and Marine. They deal in all the GM EFI stuff and would have everything you need for a swap.

**isabellsdad** · 02-10-2015, 08:24 AM

Thanks for the replys. Ive looked into plug n play harnesses but just don't have a few hundred to spend on a harness. I guess I will figure it out.

**Firebirdjones** · 02-10-2015, 09:22 AM

Yeah, understandable. Doing it for yourself is worth a shot, if it doesn't work out, it's only your time. Keep in mind the computer from the same vehicle will need a tune right off the bat to disable vats, emissions etc...or it won't even run right. So you'll have to send that off for a custom tune, at least ~$150 or so.
I did the first couple of modified harnesses myself, and then others wanted it done. It became very time consuming and I was just too busy. In the end it got too involved and people don't want to pay for your time invested. Using $50 HPtuner credit just to turn off junk you don't need in the tune. People would crab about that too.
Then the other issue was dealing with old wiring and modifying an OEM harness, there's a good chance electrical gremlins creep up down the road. Not always, but it's in the back of your mind.
So new custom made harnesses from a vendor saved time and headache, and I knew I'd have reliability. I also would buy the computer from the same vendor with the necessary tuning done, a new MAF so no issues there, new 02's etc...just to eliminate any potential gremlins. Plug and play, starts when you hit the key and go.
With that said, several hundred dollars is well worth it. Actually all that stuff will set you back about $1500. So I tell people that stop in here wanting a retro swap with engines and OEM wire harnesses and computers that they have already purchased from a junk yard..... that I'll only do the swaps anymore with a custom made harness and computer/MAF/02's done for the application, brand new and ready to use to save time. That way I also know the setup is going to be trouble free for thousands of miles with my name on it. If they don't want to buy the harness/computer etc.. etc..., I turn it away. Unfortunately they bought and spent money on things I won't even use before they came to talk to me first.
I'll add something else when it comes to these swaps. I only do them anymore if the person is willing to upgrade the entire fuel system with an "in-tank" pump which adds close to another $800 or so to the price. I've done the inline pump stuff and they just don't last much more than 6-8,000 miles before the pump dies. They simply can't run continuous with reliability, especially in a fuel injection application where the pump needs to hold 58 psi. The issue is compounded when people like us live in a warm climate. I've experimented with this on my own swaps. Trust me, being stranded when the pump dies in 110 degree heat is no fun. In-line pumps just have a short life and aren't rated very long for continuous duty. So I just don't use them anymore for other people either.

**isabellsdad** · 02-10-2015, 09:57 AM

OK I have both trucks in front of me. The 05 is still running and driving but got hit in the rear. The 78 is already stripped and waiting for the swap. I don't have to go to the junkyard for anything.