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Builds: Brian Wires His CJ-3B


Brian has provided a very thorough look at his approach to wiring his CJ-3B. My only wish is that he had written this BEFORE I had wired my Jeep, because I would have created a mockup dash like he did.  Many thanks Brian!

Brian writes, I had a major setback in my 3b project when I damaged the valve train on my CPI engine, stopping oil from getting to the lifters. So, I had to swap engines before I could really start my test-drive shake-down period. As part of my swap, I chose to go with the TBI 4.3L V6.   What really hurt was that I almost had the wiring complete for a CPI engine, but I knew what worked for the CPI would not work for the TBI engine. This meant a major layout change was in order.

If I had to label this part of my build I would have to call it “The things Painless does not want you to know”, because I feel I was able to save well over $1000.00 by utilizing a free wiring harness I pulled from a Blazer I junked.  By working with the stock harness, I was able to use fuel pump relays and other items that help me avoid the nickel and dime effect that can add up to big bucks. I also learned some sort-cuts and where to get OEM parts to help complete the job correctly.  So, here’s my adventure ….


Because the limited amount of space under the dash of my 3b, I had to move things around from the stock location in the Blazer. Fortunately, the harness I salvaged had enough wire to do this. However, trying to rewire and do everything I needed to do underneath the dash wasn’t an option.  So, I made a mockup of the dash out of wood that allowed me to easily organize, size and create a well designed electrical layout.

Fuse box firewall bulkhead connector assembly used for mockup.

The harness enters the engine space in the same place as the Blazer.Note the valve covers, anyone seeing a nice set of center bolt aluminum valve covers for a 4.3 let me know.


One important goal of mine was to shorten some of the wires and avoid some bird nests of stock wire under the dash.  Doing some research I discovered GM uses Packard 56, 58 ,59 and Delphi Metri-pack connectors/terminals that you can buy at PCS Connectors. The advantage to using connectors and terminals “to shorten” is pretty obvious: you eliminate the potential of a splice failure; also, it looks much cleaner.

Having the right tool for wire splicing and terminal connectors is a key. I contacted a small company I was an engineer for and borrowed a ratcheting-crimping tool that you can see below. It took only three tries to get the crimping technique mastered, making my wiring appear professional. (crimping tools from PCS)

Read the entire post by clicking on the link below:


My first step was to place the fuse box. GM mounts their fuse box and bulkhead connector on the firewall by punching a square hole through the wall and mounting as an assembly. So, I created a plate to mount under the dash and installed the fuse box firewall bulkhead connector assembly on it. The plate mounts at a 45 degree angle about centered on the parking brake assembly. It also served as a mount for strain reliefs, relays and other items.

Because I mounted the fuse box firewall/bulkhead connector assembly in the dash cowl, I knew wires would have to run through the bulkhead/firewall using two holes that would be drilled fire wall, both for wires and for the EFI cable.
The hole for the EFI cable will have to be quite large and a grommet will have to be used to reduce the chances the cable would get sliced.

I had three grommet choices:
1) Use the Painless waterproof Bulkhead connector for $97.95 seen here.
2) Use a split grommet big enough to pass big EFI connectors through it for under $30.00.
3) Modify the one from the Blazer.

Not surprisingly, I decided to choose option 3 (aka the cheapest option).  I took the OEM grommet and split it down the center on one side then hogged out the inside with a Dremel Tool equipped with a sanding drum. I used Zip Tie’s to put it back together in the jeep. I figured if this didn’t work I could always go with the split grommet for $30.00 as an alternative.

The GM grommets are cast on the harness (see below). The one on the left has been split & hogged out. It pops into and grabs the firewall; then the detail at the top slides over and locks it in place on the inside. I cut the hole in the firewall using a standard hole saw. (When all said and done I will silicone the wires in place as if it were cast on the harness)

In reworking the harness I kept in mind that I would be removing it for blasting and painting, so I added a pigtail connector and strain relief which allowed me to unplug the rear and front of the jeep’s harness.

Having the mockup was a pleasure being able to work at it from every angle was a good thing. When I had moved and cut it down. I installed the harness and it fit like a glove!  The fuses are accessible from the passenger side.


Though I didn’t use them in the Jeep, I kept the instrument cluster out of the Blazer and used it to help identify gauge wires I needed by plugging them into the cluster, then running each wire in the jeep and systematically cutting the wires.

The fuel gauge runs through the harness, see “Brian builds a sending unit”. I tapped into the harness for the turn/hi-beam indicators. The yellow light on the dash is the battery indicator, which is nice because it lets you know the key is on. I am running two oil sending units because there is a low pressure cutout switch. The temp, oil and amp gauge are independent of the harness except for lights. I still have to add a brake warning light and tap into the harness for the check engine light because of the computer fault codes.

All in all there is a lot of wire behind the dash. When I installed it the engine fired right up and we have not looked back.

1. has wiring diagrams for my harness.
2. “Haynes Repair Manual 82-93” had good wiring diagrams. (I learned GM really did not reinvent the wheel from model year to model year “82-93”.)
4. GM Shop Manual
5. Chilton’s


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