I have a 2003 Ranger Edge with the 3.0L. I drove it for years. Loved it. I didnt treat her so well though and several years back I blew a rod and let it sit for 4 years. Last month I was auto shopping with my Dad, who was driving me around in his 2004 Ranger Edge with the 4.0L when we were hit from behind totaling his truck. We savaged it from insurance and now I plan on swapping them out. Mine had 140k on it, but his has only 51k miles. Both engine and tranny are in great shape and I've hired a mechanic to do it. However, he is several days past when he was supposed to start and I think he is scared about the wiring harness. If the harness is good, as well as engine and tranny, what difficulties might I expect? I'm sure it would be easier to do the 3.0L, but I have a free 4.0L so the additional cost for wiring harness or whatever is ok. What should I be doing? Planning? I am ignorant to this work, but want to make sure I know the scoop so I dont get worked over and also have the best I can have. Worst case scenario I could possibly trade this motor for a 3.0L if there are businesses who do that. The motor going in is pristine though and I'd prefer the additional power from the 4.0 as opposed to the 3.0L. THANKS I ADVANCE FOR ALL ADVICE. NO MATTER HOW SMALL. THANKS.

This is the donor truck. Everything is ready to come out

 

The 2004 is an issue, and they are BIG issues not small ones
First year for the HEC(hybrid instrument cluster), the HEC is part of the anti-theft system, so not sure how much of the wiring will need to be swapped.
And first year of the SJB(Smart Junction Box), newest Body Computer, runs all the cab electrics

The 4.0l computer won't work without the HEC plugged in, and visa versa, so 2004 and up you couldn't swap clusters, this was to prevent the odometer roll backs common on Rangers and Fords in general
SJB is in the passenger side kick panel and needs to be brought over to the 2003 but problem is it was an option based Body Computer.
1995 to 2003 Rangers used GEM(generic electronic module) as body computer which was easier to deal with

I would be tempted to swap in the engine and trans and its engine wiring harness to the 2003 and then send out the 2004 PCM(computer) to be reprogrammed, or get a used/refurbished 2003 4.0l PCM, and forget the HEC cluster and SJB

The 2004 has a more elaborate CAN Bus, "network" that connects all the modules/computers, so any problems can be seen and driver notified, things like ABS, seat belts, air bags, ect..................have their own modules, and before they just had a warning light on the dash, I think they all "talk" in 2004 and up :)