Wiring swap - what do I need to know

Folks, I have what I assume is a relatively straightforward question regarding wiring.

I am pondering a 7.3 idi or idiT swap for my ‘93 f250 that has a 351w with manual trans.

What I would like to know is:
Do I need to re-run all the wiring for the truck from the diesel counterpart or is it mostly plug and play*?

Any real differences between the 88-91 to 93 wiring or is that a disaster?

For an auto trans, would I just cap off the auto wiring or?

*Im assuming I need to swap the dash, mostly due to Tachometer but I am not positive.

Thanks!

That's a toughie. I would want to swap the whole wiring from the IDI truck over. Yes the tach is different, but you also have the fuel and emissions systems (351) to worry about. The HVAC controls will be different. Probably just about everything in the interior will be different. I honestly don't see how very much at all would be plug and play. Yes, I did put an IDI in a Bronco, but at least it was Bull Nose to Bull Nose. I thought it was still a pain and I did swap the entire wiring harness.

It would be possible to move an earlier wiring system into the later truck but it would be way more work than finding a similar year truck to get the wiring from even if you get an earlier engine and transmission. Even though the circuits for the earlier trucks are basically the same as the later ones there were a number of changes in the wiring harnesses and how the circuits are laid out between the body styles. Swapping from gas to diesel adds a whole additional layer of details to get worked out regarding the fuel system. If you are serious about this big of a project, save your self some future headaches by getting as complete a harness set as you can get from a donor truck or two of your year. And get the factory wiring diagrams for yours and the donors. It's still a bunch of work but you'll minimize your distress when it comes time to hook it all up and make it run.

Wasn't 93 when they went to the electronic speedometer?

What I would do is get a set of 1993 diagrams. I would do light modifications to the original gas harness to make it work.

I would find the ignition hot wire for the gas engine. Re-wire that to the injection pump.

There is a guy on here who sells a glowplug harness and a relay. I would install that and use a manual button. If you don't like that idea, then use your original glowplug controller. It will need the ignition hot wire, and few wires to the dash light, and some heavy wires to the starter solenoid on the inner fender.

The first thing that will happen after the swap, it's not going to crank. You need to find the two red/blue wires going down to the automatic trans wiring, cut these wires and twist them together. This is the neutral safety for the automatic which won't be there anymore.

Re-use the wiring to the A/C compressor and the alternator. If the alternator is different, see what would be easier, retro fitting it to the idi brackets, or using the old idi alternator and having to re-wire. Ford changed alternator styles from year to year, so hard to know what you will run into with that.

You may be able to use the fuel injected supply and return fuel lines, but you probably need to go into the tank and take the electric fuel pump out. If you have dual tanks, you are going to have to redo the switching valve. The fuel injection used a mechanical switching valve that works off the pressure from the fuel pumps. You won't have that anymore so you will have to wire in one of the old style 6 port switching valves.

franklin2 said:

Wasn't 93 when they went to the electronic speedometer?

Click to expand...

Now that I truly don’t know.

I do however have the 1993 factory service manual with Diesel components so I can always look up the wiring. Granted its a convoluted read compared to modern rigs.


What it sounds like, is the easiest option is a 92-94 idi with manual trans. In that case I probably will swap the wiring over, along with fuel tanks and everything else. Ill just have to secondary label each wire/harness piece. Nothing new, probably easier compared to the most recent car I pulled a dash and engine bay wiring from and replaced.

My 92 has an electronic speedometer.

Takes almost nothing for wiring an idi, I would remove un needed stuff from the gasser harness.....

Idi only needs 1 wire to run. Ac compressor 1 wire. Obv oversimplifying but still. Alternator can be 1 wire. No clue on auto stuff or the electric speedo/tach stuff. I'd adapt/cut/splice the existing in my opinion.

Glow plugs, you could add a dash button to do em manual, or tap into key on like ford did with the automatic controller. You'll need the wiring to the glow plugs and controller, and the starter relay probably. If all you are transplanting is a motor, thermal controls stuff shouldn't matter but I'm no pro.

Power to ip fss, glowplugs, starter is all it takes to get these going... manual trans or c6 would be pretty easy, e4 wiring looks simple too. Probably want the cluster from the diesel...

rhkcommander said:

Probably want the cluster from the diesel...

Click to expand...

I wouldn't do that. Trying to mate that up to the newer wiring could be problems, along with the cable speedometer in the older cluster.

The 7.3 glow plug controller is basically "plug and play". You don't *need* the glow plug light; literally just hook up it's main power wire to Battery +, and the red ignition wire(small terminal on the solenoid) to key switched power.

On a OBS IDI/IDIt(92/93), you can literally just leave the existing wiring harness not plugged into the truck, and attach battery power to the big glow plug solenoid terminal, switched power to the small terminal... and everything(but the starter) will work perfectly(the cold idle, FSS and glow plug supply are all on the same circuit in the harness).

Other stuff - AC, gauges etc... optional, not needed to run.

i am currently working on getting my 84 roadworthy, from basically no wiring at all. i will say it does take time, and some ability to plan circuits ahead, but i wouldnt call it hard work. its just being on top of the engine compartment, contorted under the dash, or under the truck playing with wires. If you like wiring, the whole project might be pretty enjoyable. if you dont, i would guess you could still make it all work, it just might fall from your priority list. how much time you can have the truck out of service is a factor as well.