I'm at the point now that I have to figure what to do about the differences in the engine wiring harnesses. My truck is a '90 F250 that had a 5.0 in it. My donor engine (5.8) came out of a '92 F250. The main visual difference in the harnesses is that the 5.0 harness uses (4) small square plugs to connect to the main wiring harness on the drivers side fender well and the 5.8's harness uses (1) large square shaped plug to connect to the main harness.

How do I get this to work? From what I've read during my research on the swap the 5.0 harness used on the 5.8 will result in the injectors firing at the wrong time. I have a correct 5.8/manual ECU to use, I just need a bit of help to figure out the best way to get the correct harness for the engine.

Thanks for any help!

 

You're wasting your time here, there is no need to change any of the wiring for this engine swap, simply plug the 5.8 engine into the existing '90 engine wiring harness and attach a 5.8 computer, that's it. All the sensor and actuators are literaly the same and in the same places on both motors so none of that needs to change, and the computers are also wired the same so the '92 EEC will work with the '90 harness. Firing order doesn't matter with the batch fired EFI system either, injectors on both 5.0 and 5.8 motors are wired to the computer the same way.

 

^^ Haha, hey thats the same pretty much the same thing I said in the other tread. lol

 

Conanski,
the issue w/ the 5.8 harness is that it doesn't use the same type of main harness connection that the 5.0 uses,
so it sounds like I could use the 5.0 engine harness on the 5.8?

 

I think the issue your having is between the 90 and 92. My 89 used a different firewall plug than the 92 cab i swapped on. see if theres another plug to seperate it farther up.

 

I didn't see any additional connectors before the firewall, so I'll just swap over the 5.0 engine harness on to the 5.8 so everything plugs together the way it should. I found a bit of more work that I need to do, while I was looking over the 5.8 I noticed a manifold bolt that was sticking up a tiny bit, so I went to tighten it only to find that the bolt had long ago corroded in half only to be RVT'd in place by some hack-*** wanna be mechanic. Upon removing the intake to fix the broken bolt I found 2 more that were the same way, they were just glued in place to LOOK like they were installed...

 

lol that sucks!

 

I want to swap my 95 5.0 with a 94 5.8 both fuel injected. Can i use the computer and wiring harness off my 302 or are they different

 

That's irrelevent because you don't need to change the harness.


DING DING DING.. we have a winner!

 

Is your '95 mass air? If so you don't need to change anything(wiring or computer) simply put the 5.8 motor in where the 5.0 was and connect it to the existing 5.0 harness. And just to be clear that means remove the upper intakes from both motors and unplug ALL wiring attached to the engine right at the sensors and injectors, DO NOT leave ANY wiring attached to the donor motor and DO NOT remove ANY wiring from the truck.

 

I am doing the same for my sons 87,have 90 302 doner harness and doner 94 5.8 motor but going with man trans and both doners are auto.Do I just then need to get man trans 5.8 computer? And what will work?

 

What's wrong with the '87 harness?


Yes.. or a 5.8 computer from a trucks with a C6 auto.

 

Nothing but it is man trans 4.9,sorry forgot to say. Will that work with 5.8 and5.0 harness? Already have those and thought rather than modify harness just use them and use 5.8 computer.Will the 4.9 computer work with 5.0 harness and run 5.8? thanks for the help.

 

An '87 truck will have a unique harness on it regardless of motor so you're going to have some work to do anyway, if you have a complete V8 harness(engine all the way back to the EEC) from any year after 1988 then that will be the better one to use with a 5.8 computer.. which you will also need. And again to be clear you cannot mix portions of two different harnesses, it has to be a complete unmolested package from the motor all the way back to the computer.

 

Yes I have complete 90 auto truck 5.0 and complete 94 auto truck 5.8 will use 5.0 harness on 5.8 because 94 has diff plugs and find 5.8 man trans ecu. What ecu's will work? Thanks