Bronco II 4.0 swap wiring problems. Help me


Joined
Apr 11, 2026
Messages
2
Points
1
City
Westminster
State - Country
CO - USA
Other
Toyota sienna
Vehicle Year
1989
Vehicle
Ford Bronco II
Drive
4WD
Engine
4.0 V6
Transmission
Automatic
Total Lift
Stock
Total Drop
Stock
Tire Size
16
Hi all,
I’m helping a friend of mine finish the engine swap he started years ago. Originally the guy who did the mechanical work cut the plugs out and basically took the money and ran. I’m here to help and it’s a mess. Everything explorer is out of a 1991. I’ve followed the tech guide that James Oaks authored and am running into a few problems. I have it turning over but not firing.
1. Pk/blk from Ex harness I can’t find the mate. Can I run it under the passenger side dash to the pk/blk wire from inertia switch?
2. Alternator idk where to start cause he keeps it real cryptic in his original post. “Contact me for wire colors” anyways I’m just gonna try the diagrams see if I can figure it out or it’d be stellar if someone that knows could tell me.
3. Blk/lb wire from big white plug says to find over on passenger side. Idk I’ll try to find it but again any help would be appreciated.
Pic is of how I’m trying to make it work and look decent still in progress but got a plug out of a f-150 that has 14 connector so almost all wires are going through it now.
Please help any suggestions or advice is welcome.
 

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What year is the Bronco II?

Black/pink iirc is for reverse lights. It has been a long time since I did the swap.

I had problem with alternator exciter wire right away. Turned out i removed a fuse i needed. Did you use explorer fuse box?

Why is your picture called rats eat?
 
It’s an 89 bronco.

I’m not sure what fuse box was used. I believe it’s the explorers.

Auto correct lol I was trying for rats nest…

Looking at the inertia switch under the dash the two wires leading into it are dg/y and pk/blk.
One of the only wires I have left on the EX harness is pk/blk. Also Jim’s wiring tech sheet for this swap labels both vehicles as pk/blk = fuel pump. I want to know if I can run it through the engine bay and splice it by the inertia switch to make the fuel pump pump. Or is there a better option?

Also forgot to mention mines an automatic.

And the red wires were mixed up. Do I need to trace them so as I can get them to the correct place? Or is red just a common wire that runs multiple functions and it doesn’t matter?
 
Black/pink iirc is for reverse lights. It has been a long time since I did the swap.
That is correct. But he is dealing with pk/blk.

Primary color is listed first. Stripe (marker) color listed second.
 
The blk/lb wire goes from the coolant temperature sensor to the temperature gauge in the dash. Not sure which end of that you can't find.

Engine will run without it be ause the engune uses a different 2-wire sender for temperature. The blk/lb only serves the instrument cluster.
 

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