Jeep Hauler 1990 K3500 Dually

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Hi all. New member here. Typically I am a Jeep guy, but I needed something to pull the trailer with my Jeeps on it. When it comes to trucks, I've been a Chevy guy for a long time. I picked up a dually 1990 K3500 with the 454 and TH400 for $4,500. It is a standard cab, flat bed with the "short" wheelbase. It was an old plow truck for a landscaping business and they were upgrading to a new model. I sold the plow for $1,000 and am now trying to work out all the issues with the truck. There is certainly good and bad with it. The good is that the body is pretty clean. It needs a door panel, glove box door and a headliner. The engine, transmission, transfer case, tires, ball joints, CVs, etc were replaced in 2020, 11,000 miles ago by a reputable local shop. The bad is that it overheats and the wiring is absolutely butchered. Unfortunately their in-house guy did all the wiring. While removing the plow I found multiple splices in wires, wires that were just twisted together and taped, cut wires going nowhere (but still exposed), and even melted wires. The grill and lights are just sitting there with no fasteners (broken plastic mounting tabs) and the lights don't work since he just cut the wires to the lights to wire up the plow lights. The gauge cluster was just sitting in place and most of the gauges don't work. The reverse lights and trailer lights don't work. The wires to the fan were damaged so the fan wasn't working which could be one reason it was running hot.

I'm just here to read and research but thought that I should introduce myself in the event that I have questions going forward.

I have ordered a Dakota Digital gauge package with fan controls, transmission temp and transmission position indicators, new door panels, used glove box door, new grill and front lights. While I wait on parts I am just doing the basic tune up and maintenance items (plugs, wires, cap, rotor, air and fuel filters, oil change, etc..

Is there anything else I should check out, inspect, change or known "gotchas" in this thing before putting it to work?
 

Road Trip

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...The bad is that it overheats and the wiring is absolutely butchered. Unfortunately their in-house guy did all the wiring. While removing the plow I found multiple splices in wires, wires that were just twisted together and taped, cut wires going nowhere (but still exposed), and even melted wires. The grill and lights are just sitting there with no fasteners (broken plastic mounting tabs) and the lights don't work since he just cut the wires to the lights to wire up the plow lights.

I'm just here to read and research but thought that I should introduce myself in the event that I have questions going forward.

Greetings Off Grid,

Sounds like your first stop should be the .pdf versions of the Factory Service Manuals
for your '90 K3500. Check it out over here: ('88-'98 Service Manuals) Be sure to
download the electrical manual, and it will help you get that wiring harness back to
a reliable condition.

Elsewhere in this forum we've got some guys who really demonstrate how to make
the cooling system work as good as/better than new. Keeping your big block cool
is both doable and highly desirable for long term reliability, so look up what the Texans
are doing to their cooling systems and you should have plenty of ideas of what to do.

And welcome to the GMT400 forum. Always nice to see another big block owner
joining in.

Cheers --
 
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Thanks everyone. That is all very helpful. I just downloaded those pdfs.

What wiring harness do you recommend? There seems to be a lot of options out there. I was looking at this one for the engine, but didn't really see a good one for the chassis. I should also mention that when they put the flat bed on it they just hacked into the wiring for the lights. So all that needs replaced as well.
https://www.speedwaymotors.com/Pain...ottle-Body-Injection-Engine-Harness,8540.html

I know of at least two issues to the overheating. One is that the electric fan isn't working and the other was that huge plow on the front. It was completely blocking the radiator. Lowering it a bit would help, but I don't need or want it, so that is gone completely now. I'm on the lookout for other contributing factors now to cooling issues. I'll give it a flush and check out those Texas guys.
 
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Ok, I actually found a different part number for the chassis wiring harness. This one has provisions for power windows and locks. Also, I called Painless Wiring and they official answer is that they don't make a kit for these trucks. That being said, they also would not say that it wouldn't work for these trucks. So that means that I'm basically on my own. Oh well. Here is the kit I am ordering for the chassis. This is along with the harness for the TBI control.

I do have some questions for you guys though.
* How are the heater controls in this thing? I am hoping that they are pretty self contained and that I can just supply the "system" with a +12v power wire and it will function. From what I can tell is that it is all electrical and not vacuum operated. Can you guys shed some light on this?
* Same question for the radio. Although I may replace it with an aftermarket unit. That is not real high on the priority list though.
* This has the TH400 transmission. Is this the NSS at the bottom of the steering column? See picture with the red arrow and circle.
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Erik the Awful

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The A/C harness is a separate harness that plugs into the main harness. My harness on WCJr was pretty hacked up by a previous owner, so I nabbed a junkyard harness and installed it. That's probably your best option.

Roscoe's a whole 'nuther level of terrible. The truck was full of mouse turds when I got it, and all the wiring was chewed up. The local Pull-A-Part sells harnesses cheap, and I got a whole set of harnesses from various trucks - none were entirely intact. I then sat down with a bucket of splice connectors and mixed and matched harness bits until I had a good harness. Even that will be less work than installing a new harness from scratch. You're going to be spending a lot of time adapting the factory components to the Painless harness.
www.amazon.com/gp/product/B07L29DLGN
 
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Thanks for the link to the butt connectors. Those look nice. I'll order some up.

Do you happen to know if that is the NSS in the photo?

The pull-a-part harness isn't a bad idea. Either way the entire harness in the engine bay needs to be swapped out though. The wires are in terrible shape in the engine compartment. I don't know which would be worse, a mouse eating the wires or Bubba with a pair of wire strippers. One of the problems I have is that they aren't just cut, spliced or melted. There is also a bunch of extra wires added that I need to track down and remove. Some just dead end and were for a past modification that has since been removed, and others go to non-working devices like light bars and such. So no matter what, I think I am going to have to trace down each one and either remove it, replace it or re-terminate it. The dash wires for the sound system and heater controls look to be untouched though.
 
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So I ordered everything except the chassis wiring harness. I still wasn't sure which one to get. I was thinking more about the fact that it needed to be "universal". Then it hit me. I already have a new universal wiring harness for another project that I probably won't get to for another two years (1972 Jeep Wagoneer). I have too many projects. So I pulled the wiring harness out of the shed and I think it will work well. The TBI harness should be here Monday from Summit. Although I have other obligations that will probably take a lot of my time for the next month.

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