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Painless CJ-5 Rewire

Posted in How To: Electrical on April 1, 2019
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“That light’s still not working,” I yelled to the owner. He spit out a string of obscenities, cursing whatever electrical demons had possessed the Jeep. The electrons were once again dancing like banshees and not at all heading where they needed to go.

Aging Jeeps can start to suffer, with regard to reliability, even when they’re well maintained. Parts age and systems fail despite ardent service and preventative measures. Electrical wiring as a system is subjected to heat/cold cycles, vibration, and exposure to chemicals and the harsh elements of weather. Old wiring insulation can become brittle and crack, while connection points can become resistive or fail due to mechanical breakage or corrosion.

The electrical system on this 43-year-old CJ-5 was suffering from some of those maladies. There were lights that didn’t work and some that did when they shouldn’t have. A previous owner had done some of his own wiring modifications, and that wasn’t helping matters. We decided the best plan for the long term was to rid the Jeep of most of the added wiring and pull the entire factory harness out for replacement.

We sourced all the parts we needed from Painless Performance, including the #10150 21-circuit replacement harness for Jeep CJ models. We replaced ground straps with braided ones and wrapped the harness wires in various sizes of Power Braid for abrasion protection and a clean look.

One can always pursue the hard work of wiring a vehicle from scratch, but we chose to use an aftermarket solution to replace a factory harness and ordered up a Painless Performance direct-fit harness designed specifically for ’76-to-’86 Jeep CJ models. The kit comes complete with an ATC fuse panel; wiring harnesses for engine, interior, and tail sections; and plenty of small parts, extra wire, and electrical terminals. With a chassis ground strap kit and DuraSpark ignition harness kit, there was almost everything to fully rewire the whole Jeep (except for battery cables).

Painless provides a thick reference manual with very detailed instructions on how to rewire the entire vehicle. It includes notes on model variations, how to incorporate aftermarket electrical components, and specifics for wiring a fiberglass tub. Another nice feature of the 148-page instruction book: the full descriptions of each wire regarding its function, size/color, and termination points. This is useful both during installation and later should you ever need to do wiring modification or troubleshooting.

We began by stripping all the existing wiring from the CJ-5 and removing the dash for easier access there. Then, we started installation of the new Painless harnesses using the reference manual as a guide. This process takes time, so it pays to be methodical and understand how the harness is going together.

The interior and tail harnesses are laid out plainly for the most part. The engine compartment harness will require more custom routing and wiring, depending on what you have under the hood. We started from the bulkhead connector and worked our way to the passenger side and forward, wiring items as we encountered them. Keeping the wires bundled and taped with electrical tape every 6 to 8 inches helped keep the wiring organized. When you find you want to reroute or you’ve missed something, cut off the last few tape wraps and rework the harness routing going forward.

We did some function checks to confirm all was working well. Once complete, our entire electrical system looked so much cleaner. Plus, we had confidence that all the electrons would be dancing to our tune and going where they needed to be when we’re out exploring trails in the Jeep.

Our wiring had been slowly degrading with age, especially those wires subject to underhood heat. The insulation was losing its flexibility and there were signs of copper corrosion in some locations.
We began by stripping the old wiring out, making note of the original routing and trying not to damage any of the original connectors in case they needed to be reused. This Jeep also had a lot of patched-up wiring that had been added over the years.
Painless recommends at least pulling the dash forward a few inches to access the wiring behind it. We chose to remove it completely, removing the steering wheel with a puller and disconnecting the heater box cables.
With the dash removed, working the harness out from around the steering column was easy. This CJ-5 has air conditioning, and we just left the unit mostly in place. This was a good time to inspect and replace old heater and defroster parts as well.
It can be helpful to label old connectors as they're removed with the Painless-supplied labels. It’s wise not to throw away any of the original harness until the rewiring is complete. We referred to the old harness several times to confirm wire colors or connections while installing the new harness.
Here you can see the original fuse panel with glass fuses. The new Painless panel uses bladed ATC fuses, which are easier to use and more reliable. There are turn signal and hazard flasher modules, and a horn relay, on the new fuse panel.
The new fuse panel fits cleanly in the stock location, but it may require enlarging the two mounting holes where the new fuse block is bolted to the firewall.
The fuse panel mounts from inside the firewall with a seal gasket. After applying some dielectric grease to the fuse panel terminals, we mated them to the engine-side bulkhead connector.
Most of the harness is terminated with new connectors that plug right onto your various components. However, it’s necessary to add terminals to some wires, or reuse an occasional stock connector in some cases. As such, it’s good to have a handful of wire cutters, crimpers, and strippers on hand. The Painless manual has recommendations and detailed crimp instructions.
We used the provided 6-gauge wire and terminals to build a new alternator feed wire. The kit also includes heat-shrink tubing and a new terminal boot.
This Jeep had an old thermal-actuated choke that didn’t work well. We upgraded to an electric choke easily, as the Painless harness had wiring for one.
While we were going through all the electrical, we swapped from stock halogen headlights to newer H4 housings. To ensure maximum current to the new bulbs, we installed a Painless Headlight Relay Conversion Harness to get power more directly from the battery. To keep the engine bay cleaner, we hid the relays inside the grille shell behind the passenger-side headlight.
We also added a weatherproof CirKit Boss auxiliary fuse panel on the firewall to provide additional circuits for added lighting, ham radio gear, and other accessories. Power supply wiring was routed to circuit breakers near the battery. Other wiring was routed through an added grommet into the Jeep interior.
With the dash out of the Jeep, it was easy to look over all the switches and other electrical items. We replaced the old headlight switch and dash label lights, and confirmed our stock instruments were in good condition.
The new interior harness was routed over the steering column and laid out in preparation for the dash install. It’s a little easier doing this with two people so one can hold the dash as the other installs bulbs and connectors.
The tail harness services everything on the rear of the Jeep, including stoplights, turn lights, taillights, and a trailer connector. It was all plug and play, plus anchoring a couple of body grounds.
The tail harness connects to the main harness under the dash. For easy routing, we chose to remove the terminal from the Weather Pack connector using this simple tool. It’s handy for this or anytime you may need to pull terminals from a connector body.
We finished up the wiring with Painless Power Braid in various sizes. The flexible mesh sheath wraps around wire bundles to protect the wires, and it gives the whole install a professional look.

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