I have a 1999 Ford Ranger extended cab that originally had a 3.0 engine it, the block started busting after the headgaskets blew so I bought a 2001 ford ranger with a 4.0 engine but it is not an extended cab. So I've mostly got the 4.0 2001 engine in my 1999, that includes the ECU, but I am worried when it comes the wiring harness. I'm unsure of what modifications that need to be done or which harness to make the modifications to. I'm guessing that I should do the modifications the 3.0 harness sense it has the extended cab additions but again I'm just unsure. Has anyone else done this kind of swap and if not why? I'm hoping to get some direction on what needs to be done.

 

Welcome to the forum

No, there won't be much out there on this swap since it's not a good swap, i.e. same work as V8 swap but without the benefit of V8 engine

Yes, you will swap in the 4.0l SOHC engine w/transmission and 2001 computer with engine wiring harness
Change the 2 timing chain tensioners in the 4.0l SOHC for sure

Yes, used the 1999 body wiring harness, just remove computer and engine wiring harness and label any 12 volt and ground wires from 3.0l harness that had to be cut to remove the rest of the harness

Fuses and relays will be 1999 and you want to keep it that way for future servicing

Best thing to do is to get the Ford 1999 Ranger "wiring diagrams" manual
Ford sends "Shop Manual Sets" out to all Ford Dealers for ALL Models every year, the "wiring Diagrams" manual is part of that set, and often sold separately
Like this one: https://www.ebay.com/itm/1999-Ford-R...2137363?_ul=IN

It covers all the wiring, colors and locations, for all 1999 Rangers, so all engines sizes and options for all sub-models
So it will have the wiring for 1999 4.0l OHV Ranger which won't be exactly the same as 2001 4.0l SOHC Ranger............but for 12volt power and grounds it should be usable

These are basically "free" to use because you can sell them for what you paid for them, in most cases