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Hey guys. I’ve spent the last year or so swapping a 5.3 vortec and tremec t56 magnum into my 78 camaro. The swap is all finished up, and i’ve run into some electrical issues.
When I turn the key to run, the fuel pump won’t turn on, and when I turn the key to start, the starter won’t crank.
I used the factory harness from the 5.3 that I bought, and did a ton of research on how to do the wiring properly. After looking at many videos, forums, wiring diagrams, etc., I am almost certain that my wiring is correct.
I checked voltages, and in run and start positions, the pink wire going into the white connector of the fuse box is getting 12v. And in start position, the yellow wire going into the same white connector is getting 12v. I know my starter works because I can jump across the terminals and get it to engage. Also the fuel pump should be fine as it’s brand new.
I hate to be that guy, but it seems like the computer is the issue here. It doesn’t seem to want to do anything. Maybe the people who I sent it to in order to get VATS removed fried it?
Anyways, any help is much appreciated, and of course, let me know if you have any questions. Thanks for your time.
So I will take a guess.
So the no crank part you may have an issue with the neutral safety switch? both with a manual and auto 78. The manual trans of that time had a clutch pedal safety switch. Unless you press the clutch pedal it won't start. Easy enough to jump out. That wiring should have nothing to do with the LS wiring harness. When you turn the key to start it should show 12 volts to the start terminal on the starter. Not sure about an auto NSS but it's either on the column under the dash or on the console shifter.
Don't know if you are using the stock 78 Camaro wiring harness but on my 80 LS swap I used the HEI coil wire as my 12 volts in start and run.
The fuel pump should run for a few seconds with key on but not turned to start. You could try to "hot wire" the fuel pump with temporary relay and wire directly to the fuel pump after you get it to crank.
On al my LS swaps I've never "burned up" LS computer. But because I suck at electrical I always buy a ECM and harness from one the great suppliers on this web site.
About the NSS. I thought that might be an issue, so I just spliced the wires together. That wire then comes out through the firewall as a purple wire, and while I could just run it down to the starter, a bunch of stuff that I read told me to run it to the yellow A3 wire in the white connector of the fuse block. So that’s what I did. That wire is hot in start, but not run, which is how it should be.
About the fuel pump, that’s a good idea to test it out. I’ll do that and see what happens. My power wire for the fuel pump comes from the grey wire in the corner of the red connector.
Finally, the pink A9 wire in the white connector is from what used to be the HEI. It’s hot in run and start, as it should be.
I didn’t modify the black connector.
The image below shows everything I just talked about.
I would try running the purple wire directly to the start terminal on the starter and see if it cranks.
Your fuse block shown above looks nothing like my 80's fuse block. My 80 has blade type fuses.
are you sure the ecu is getting 12v where its supposed to be getting 12v? you talk about a white connector but not the connectors that actually plug into the ecu.
you can also pull the green fuel pump wire from the ecu and put 12v to it to see if the fuel pump turns on.
Left town today for an internship, so I won’t be able to troubleshoot for a while. When I get home I’ll try what you said about the starter. Thx for the advice.
And yea i guess the 80s ones are totally different than mine. Thanks for trying to help tho. It’s much appreciated.
That’s a great question. I connected the blue and green connectors into their correct locations in the ecu. I remember double and triple checking that. I’ll check again when I get a chance tho.
Do you know the pin out of the green fuel pump wire that you are referring to? No worries if you don’t. I’m sure I can find it in a diagram somewhere online.
As for where I put the 12v in run and start, I just wired it to A9 in the white connector because that’s what I saw people doing online, and it worked for their swaps.
If it was me I'd strip the harness down to the bare essentials and install it into the car, run the smallest fuse box needed with the minumum relays. That factory truck one is way over complicated.
When a fuel pump doesn't run as expected, locate its relay, removed it and insert a jumper between pins 87 and 30. If still no fuel pump, there is either no power to the relay, or its not connected to the pump. If pump now runs, its either no signal to the relay, no ground to the relay, or the relay is bad.
I agree with @the_merv that is is better to either strip down the harness and use a small fuse and relay box, or an aftermarket harness. The OEM harnesses have zillions of wires never used in swaps.
My go-to has been 4th Gen Fbody, 1995-up. That factory Fuse Box works perfect for swaps. One in my MCSS is from my 1998 Camaro, when it was wrecked I scalped it for parts to build the MCSS.
My go-to has been 4th Gen Fbody, 1995-up. That factory Fuse Box works perfect for swaps. One in my MCSS is from my 1998 Camaro, when it was wrecked I scalped it for parts to build the MCSS.
From your picture, that looks like an excellent suggestion. The factory fusebox is likely much more water resistant than any aftermarket one.
From your picture, that looks like an excellent suggestion. The factory fusebox is likely much more water resistant than any aftermarket one.
My goal was to make it look factory and to do that need factory GM stuff, that and they work. The wiring is the same color so it's Army proof. Just put in the time and understand what the wires are for and you're good. Little bit of creating my own circuits here with some of it but it's knowing what wire does what that helps. No more fuseable links, battery power comes into that Camaro Fuse Box and the large Blade Fuses are on everything Red 12v Constant going to the interior. From there the Ignition Switch splits it to 12v Key-on Ignition and everything else factory setup for the car. Fans are controlled too, as well as Starter and Fuel Pump with Relays in that box. All LS Engine Harness stuff comes from that Fuse Box just like the Camaro did.
Runs perfect and been running perfect since 2010, do it once do it right.
Old pic but to back my suggesstion. This is a 1991 S10 I crammed an LS1 & Built 4L60E into back in 2012. Used the Fuse Box from a 1996 Camaro, it's right behind the Air Filter. They are literally a rectangular block with everything needed and it's own mounting bracket so if you're tight on space this is an excellent one to use. Has it's own cover too, again factory look.
05-13-2024 | 08:02 PM
78 Camaro LS Swap No Start 
