So I'm in the midst of pulling my 5.8 out of my donor truck and have a question about the electronics. I pulled the computer out of the 5.8 truck and was wondering, do I just pull my 4.9 computer and swap em? Or do I need to re-pin any of the pigtails? Also I have the engine harness detatched at the "power center" and was wondering the same about this. Since it's going into a truck that originally had a 300, can I just plug it in or will it not work that easy? The catch is a freind of mine wants the donor truck and the 300 so I can't really just go choppin wires or anything. Thanks guys!

 

Lift the 4.9L engine bay harness out and lay in the 5.8L harness. Then you'll only have to modify the dash harness slightly. The Haynes manual diagrams show the differences.

 

Ok, does that include the relay box? The trucks are identical other than the donor has power locks/windows. Sorry, I'd check my haynes book but it's in the barn I'm workin in (about 20 miles) and I just left there lol. Are you saying unhook the chassis harness at the firewall and take all the rest? That made the most sense, but I didn't feel like rewiring the power locks and windows while I was layin into it so I held off on that.

 

The locks/windows harness isn't part of the engine or engine bay harnesses. It's inside the cab. Unhook the engine bay harness at the firewall and swap it along with the engine.