So, I'm planning on custom building a wiring harness for my 86 F350 Chassis-Cab. Main reason for this being the current wiring harness is almost entirely shot. Between corrosion within many of the wires (deep through the sheathing of the wires) and breaks in the wires, and melted sheathing in various spots thruout, I have decided that a brand-new, simplified harness is needed.

This leads me to the first bit of advice that I'm seeking on this topic: the fuse box.

Since I'm wiring everything custom and simplified, are there any fuse boxes currently being sold that would work for my 6.9L IDI diesel? I contacted Painless Performance, and they say they don't have any products that would work for a diesel, yet their standalone fuse box looks like exactly what I need.

Also, just so everyone knows the direction this wiring project is going, I'm planing on a centralized wiring system. basically, a large 8 gauge wire brings power into the center of the cab thru a bulkhead connector, and the fuse box, which will sit inside a police-style center console towards the front of the cab, distributes the power to the switches, lights, gauges, etc. I am also thinking about putting the relays in this area as well, but that may change if I find a relay box that will look good in my engine bay.

Anyways, any advice on the fuse box dilemma would be a huge help!

 

The painless should work whether it is gas or diesel. No matter what you do you will still need to deal with the exceptions (the things painless harness doesn't cover).


I would also consider going to salvage yard and looking for a correct harness. Unless the truck was underwater there shouldn't be too much corrosion on the connections. It's easier to repair/rebuild a "correct harness" in the comfort of your home then install when ready, then to do a complete rewire (one wire at a time) out in the yard.

 

awesome! I will probably end up doing that, then. shouldn't be too hard to add circuits that they don't cover.
well, the history of this truck: it was a rescue truck out at the Bonneville Salt Flats. the wires are not only corroded at every connector near an exterior panel, but several of them corroded thru the connector along the wire inside the insulation.

and that extreme level of corrosion is exactly why I'm replacing the harness outright. the other issue with a junkyard harness is the same as my issue with finding belt brackets: no junkyard in my area has these diesel trucks. they're all gassers.

 

So, my wiring was butchered at some point in it's past. And I think that's the culprit for the engine struggling to start. Everything tested good, except the voltage regulator which I replaced. And it's still having the same issue.

My question at this point: does anyone have any expertise wiring up an old 6.9? I need to start from scratch simply because it's been so butchered and it's so damaged by corrosion that the original harness can't be saved.

 

Look at the Electrical, Vacuum, Troubleshooting (EVT) manual on Gary's Bullnose forum/website. You should be able to find everything you need there.
Here's the link http://www.garysgaragemahal.com/evtm.html click on the "86 EVTM" link

 

I hate to be blunt, but if you are asking this question you are probably not ready to tackle a job this big. And it would be big.

I don't like those universal harnesses, they do not come with plugs that plug into everything. Too much custom work, too much soldering and shrink wrap.

I really think you should beat the bushes and look for a old harness in good shape. I think it would even be easier to get a gas truck harness, lay it out side by side with yours, have the diagrams for both, and modify the gas harness to fit your diesel.

The main difference in the diesel will be the wiring at the starter solenoid, and the wiring for the glowplugs and the few wires that are on top of the engine. If you get rid of the factory glowplug system which was prone to failure anyway, and wire a manual system in place of it, that would simplify some of the wiring.

Your idea of a complete redesign into the center console is interesting, but I am getting hints that you will not be able to carry it through to the end. It would be a lot of work for even a experienced vehicle electrician.

 

Youre right. It's a huge job, and I'm out of my element here. But I would prefer to keep this truck running, and make it what I want, rather than replace it with a newer truck. And to keep this thing running, it needs a new harness. Plus, I've been toying with the idea of a Cummins swap from a medium duty box truck. If I do the swap, it'll need different wiring anyways.

And to help understand why my wiring is messed up, take a look at this rats nest of wires.

 

Keep looking for a diesel harness, but I think my idea of using a similar year gas harness if that is all you can find, would put you way ahead of the game. You know the light wiring and the heater/A/C wiring is the same gas or diesel. And all the wiring to the rear should be the same if you have a diesel truck and gas truck, same or close in years, both with dual tanks, etc. There are minor difference though, so write in and ask. For instance I think a carbed harness would work better for you than a 85-86 EFI harness. The 460's and 351w's were still carbed those years. The 460 with dual tanks is actually the same wiring as the diesel for the dual tanks, both had a return fuel system with the 6 port valve.