Rewiring underhood from FI to a carb engine

[StevenH]

89 MJ 4.0... I am putting a 4.3 under the hood, while I'm waiting on advance adapters to get my motor mounts here I am sorting through the underhood wires. I basically have the wires cleaned out, my thinking is the only wires I will need are the ones from the firewall connector, I am assuming that the other 2 points that wires come into the firewall are all FI and emissions related... was I wrong to make that assumption?

[JeepcoMJ]

not sure what the other 2 points are, but...

 

if I were you, I would run the truck with the 4.0 harness intact, remove what's not needed from the harness but use the fusibles etc. to power the interior and so you don't have to rewire your starter relay or anything.

 

then I would run your 4.3 harness (a painless one I'm guessing?) seperately.

 

you will need to use the 4.0 gauge sending units ON the 4.3 in order for the gauges to work, but that's easy.

 

when I did my 3.8 swap I used the camaro harness and pulled everything I didn't need from it.

here you can see the camaro fuse box, engine computer (it's waterproof under-hood), and you should be able to trace the seperated harnesses as well

...and the pile of wires I searched through

stock oil pressure sender but on the 3800

[StevenH]

It's too late, the other 2 harnesses are already cut out :eek:

 

I won't need the starter relay, it's already out. I am using a gear drive sbc starter, you hook the hot wire up and run a wire to the solenoid.

 

I won't need a harness either, all I will have wires going to is the coil, starter and the gauge sensors which I will use aftermarket gauges and use their sensors. And the headlight harness but I know it is coming from the firewall conector. The windshield wipers are on it's own harness that comes out by the master cylinder. This will be a rock toy and not a DD.

 

I cut the wires that come out of the firewall towards the passengers side because it all looked like FI. Chevy runs their FI injection harness out of the same exact spot. Then I got to the harness that comes out of the middle of the firewall and it was FI also because the wires that go to the injectors are in that harness... made me wonder if all of the wires were going to the FI from the first harness :D

 

It doesn't matter either way, I can wire it up no matter what. I just wanted an idea of what was in those harnesses to give me a headstart.

 

If Chiltons had the diagrams of the wiring harness in their manual I would have known this fromthe start ;)

[CEThomas]

What trans do you have? one of them is for the trans if you have an auto.

[StevenH]

th400

[CEThomas]

One was for FI and the other for the trans so you will be OK ;)

[StevenH]

Thanks! :D

[JeepcoMJ]

remember to send in a fusible to power everything in the cab and your tail lights...you cut those out too.

[StevenH]

Ok, thanks.