Wiring dilemma (behind dash)

[DThibault]

My cab is painted and I am putting the guts back in. I have a couple of questions. My original truck is 91. 5 diesel, plain jane, no power window, AC, or vacuum control heater. My donor truck is a 92 gas job with all the goodies, the color interior I want, and Power window, power mirrors, AC, everything loaded. The harness on the gas job doesn't have the info center, water in fuel, wait to start, 4WD etc. My question is: which harness do I start with and enhance with parts from the other. My gut says to try to move the info center to the gas harness. My concern is that main junction between the cab and the chassis with not be compatible. ANy ideas or experience here? thanks.

 

[Simplysmn]

well check the wiring harness from the Diesel for the power window plug the driver's side goes all the way across dash and hook's into the Pass side you might get lucky and find it has the plug there the power harness is the same on the gasser so it might be there on diesel harness .

 

[JMDancoe]

Best thing I can tell you is to get a wiring schematic for each of the vehicles. Check the circuits and see what is compatable and what is not. Your 91. 5 / 92 compatability will be much simpler than my 92 (under hood) to 86 (under dash). There is a service online that can provide complete schematics for each. They charge a fee, but it is not much and is worthwhile. I installed a 92 Instrument package in my 86 and had to basically rewire my 86 (under dash) harness to mate with the 92 (under hood) harness. Some of what you may need to do can be done at the 50 way firewall conector. Are both vehicles auto or standard trans? It will figure into the wiring, if one is auto and one is standard. Check the fuze panels for both units. Again, you may not have a problem there as the years are so close. For the diesel, you will want the message center wiring to be correct. Wish you the best of luck. It has been almost two years since my brother and I did the retro on my truck, but will try to find the name of the online service we used for the schematics and post it here.

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86/92 Retro D-250, 5. 9 Cummins w/auto, 2wd - 256,000 / 96 Ram 1500 short bed, 318 w/auto, 4wd - 323,000 / 2000 Jeep Grand Cherokee, 4. 0 w/auto, 4wd - 251,000 Dodge/Chrysler all the way

 

[DThibault]

Thanks guys, I have schematics for the 91. 5, both gas and diesel, I don't know yet the difference between the 91 and 92 gassers. At first it looks like a bowl of spaghetti and its been over a year since I took them apart so I'm looking for a rainy day when I can hide and lock the doors and go over the whole thing. I'd like to get it somewhere near right so I don't scratch the new cab up messing around in there.

 

[JHumphries]

I know the main power lead coming from the battery is bigger on the diesels.
That being said, I don't know if the wires feeding the fuse box are any bigger.
Might be else something worth looking into.

 

[JMDancoe]

I would stay with the 91. 5 diesel harness because it is wired for the message center, which you will need. If you have both out, lay them down and start from the 50 way connecter (firewall plug). Simply match them up. You will probably find a lot of what you need for the accessories you want, will be there. From the main, out to the accessory, you may have to purchase or make the individual harnesses. If you do, make a step by step record of the construction. It will come in handy later "if" you should have an electrical problem. Be sure if you make any changes to the under dash harness, that it will work with both the fuze panel and the 50 way going to the under hood harness. If your steering column has a clockspring type setup for the wiring, I hope you knew to not turn the wheel while the column was disconnected from the steering box. The clockspring device will break and those items that are in the wheel, ie. cruise control and such, will not function. You will have to replace it.

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86/92 Retro D-250, 5. 9 Cummins w/auto, 2wd - 256,000 / 96 Ram 1500 short bed, 318 w/auto, 4wd - 323,000 / 2000 Jeep Grand Cherokee, 4. 0 w/auto, 4wd - 251,000 Dodge/Chrysler all the way

 

[JMDancoe]

Just as an FYI the site name we got the schematics from is AllData/DIY. It has a fee for day's usage. Found it very helpful, so am posting it for you or whoever may want to use it.

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86/92 Retro D-250, 5. 9 Cummins w/auto, 2wd - 256,000 / 96 Ram 1500 short bed, 318 w/auto, 4wd - 323,000 / 2000 Jeep Grand Cherokee, 4. 0 w/auto, 4wd - 251,000 Dodge/Chrysler all the way

 

[DThibault]

I started to go the other way by modifying the gas harness but now I think you're right. The gas info center shared many common wires but a few like the water in fuel and wait to start go in the wrong direction. I will reverse the process, I think, I didn't mess up my clockspring as mine is a plain jane truck, the other, I don't know what. I did see the kids playing with the steering wheel. Hope this doesn;t turn out to be a nightmare, I'll be sitting in a newly painted truck making motor noises pretending to be driving around town. I do have a total diesel deluxe harness in another truck but its still running and not in bad shape so until I give up here, I'll leave it intact. Thanks again and I'll check out the site with the diagrams.

 

[HHhuntitall]

Ahhh, what's the production date?



There are several wirelooms, it appears. An early 91 is different from a late 91, and a late 92. Starting in 92, when they did away with the external voltage regulator, all your accessory wire plugs are in the wireloom, regardless of what features. The outer wire loom might not be there, like for the windows, locks, etc. But on the 91, the power window loom is not extended beyond the fuse block, IIRC. That shouldn't be much of an issue, if you have a similar loom for the gasser, as you can pull the wire feed from the gasser loom and push it into the fuse block for the diesel. Earlier Cummins didn't have a larger feed wire to the fuse block, that I've seen. The later models, without the external voltage regulator, had an 8 or 6ga feed wire, slightly larger than the earlier models, which is fed in from off the fender. It feeds the main key switch and accessories, and is a bright Red wire. I actually think there are two of them, but I don't have one in front of me at the moment.



I can't remember, I'll have to look, but I may have one for a later 91, but I can't recall if it had power windows... ...

 

[DThibault]

I have a late 91 with intercooler but it also has the external voltage regulator. I started on the project last night beginning with my old diesel harness as suggested. It seems the way to go. I laid it out above the dash and as I peeled out the gas harness, I laid in the diesel one being careful to get it set into the plastic holders where it was supposed to be. It seems to be working out fine. A lot of the stuff I didn't have in my plain Jane truck still has a plug on the harness ie the overdrive for the auto transmission. I have a manual but the harness is still post 727. I left the power mirror switch assembly in the the donor gasser dash, haven't seen where that hooks in yet.

I also left my non cruise steering wheel attached. I don't know if I'll be going that route or not. I use it on my 01 but I may just take off one of the throttle springs to rest the ankle on a trip out of town.

Its a long way from running, I still have to get a couple guys help me put the chassis back on the frame, but the harness does look promising. Thanks for all the help.

 

[HHhuntitall]

Yes, the diesel interior wire loom is the way to go. Then you can use the exterior wire loom which will include the grid heater feeds, water in fuel, wait to start, etc. Good luck!! I just got the wires in my '85 from the '91, and it's a pain matching them up..... the '91 wasn't power anything, but the '85 was top-of-line... ... those looms don't match up very well..... I've nixed doing anything to the interior wires until it comes back from paint.....

 

[DThibault]

This is a little bit different subject but along the same lines, are the ignition key switches and steering column the same between the gas auto transmission and diesel manual? I still have ideas of adding cruise control switches and the tilt wheel from the gasser. The steering column is in much better shape on the gas job too. I have another place to get the under hood part for the cruise.