Is the wiring harness plugged into the inside of the fuse block, or part of thehaharness? All the ones on eBay have the wires cut off right beside the box.
2000 f250 v10.


Of course I meant "Underhood". Love autocorrect!

 

The guy to ask would be SkiSkiJason, he does a lot of 5.4 to 7.3 conversions so has been in deeper with the electrical systems than most.

 

I'm waist-deep into rewiring a 2000 Excursion due to a left-side engine bay fire. I'm getting a good grasp on the wiring of these things. I'll tell you what I know as it pertains to your picture:

1) The underhood fuse/relay box is part of the underhood wiring harness. It doesn't unplug from the harness (it can be disassembled from the harness though by pulling out all the fuse/relay connections, but it isn't a very easy task).
2) The number for the harness assembly is 12A581. There are prefixes and suffixes to that number. Your prefix for a 2000 F250 should be YC3Z, and the suffix would depend on different things, such as options. So the harness number would be YC3Z-12A581-whatever the suffix would be.
3) It is highly doubtful that you'll find a new OEM harness. I couldn't for my Excursion. And if you do find one, it'll be in the $800 range.
4) When finding a used harness, you'll want one from a truck that matches yours to these options:
Engine
Transmission
Transfer case type (manual or ESOF (manual transfer and 2-wheel drive are the same)
Headlights- standard or Daytime Running Lights
Headlights- sealed beam or composite (though you can change plug ends if needed)
Emissions- Cali or 49-state
EGR- do you have it or not
AC- do you have it or not
ABS- 2 or 4 wheel

An Excursion harness will have an Excursion-specific fuse/relay box due to things an Excursion has that a pickup doesn't. The harness itself is pretty much the same though. If you are comfortable with wiring and diagrams, you could modify an Excursion assembly to work in a truck, by verifying pinouts at the box and removing what a truck doesn't need.

This harness is U-shaped: it goes down the driver side inner fender picking up the engine connectors, ABS system, left lights... across the top of the firewall picking up the hood light, wipers, evap canister purge valve... down the passenger side inner fender picking up the blower motor and resister, cruise servo, pulse vacuum hub solenoid, the connector to the AC harness, washer pump and right lights. There are only 2 grounds bolted to the body, near each rear corner.

Looking at your picture, you COULD go another route:
1) Get one of the boxes on Ebay with all the wiring cut off.
2) Carefully pull all the good fuse/relay connectors out of your box and insert them into the proper locations on the Ebay box.
3) Cut the ends off of the burned wires on yours and splice them into the wires on the Ebay box.

Myself, I'd probably opt for a whole complete harness if you can find one.

Note: a harness from a 99 or an 01 will either be the same or very similar. When looking at these verify every pinout-to-wire color. Ford just loves to switch pinout locations for no obvious reason.

 

Just by looking at it I figured that would be the case. I don't get why someone would hack the harness off at the box and sell that instead of pulling the whole harness out. I think it would be well worth the time since I know I'd pay more for it!
For now, I think I'll find a wiring diagram and pull the trailer running light wire out, add an inline fuse, and tie into another hot wire that's a spare in the box. Then I'll start watching ebay for a complete harness. This truck has other more pressing issues I need to address first, like the transmission torque converter lock up, or lack of lock up!
Thanks so much for your detailed reply!

Eric

 

From the photo it looks like just the burnt section( orange fuse block) of the fuse box could be replaced. If you had a used fuse box with enough of the harnesses you could just pop the orange block and solder/shrink wrap the harness back together.