Painless > OEM Wiring Harness - 1980 FJ40

[HoundDog]

I have a 1980 FJ40. It has a Painless Wiring harness from circa 2012. Everything works; however, under the dash is a rats nest of twisted together wire connections wrapped in electrical tape, and the harness is routed incorrectly. It bothers me, and is potentially unreliable.

I have an unmolested OEM wiring harness with OEM connectors sitting in a box. The circuits have been continuity tested and labeled and they all tested good.

How feasible would it be to refurbish the OEM harness, remove or repurpose the unused circuits, replace the old glass tube fuse box with a modern spade fuse box, and add a relay box to accommodate future accessories like an air compressor, etc? The truck is professionally de-smogged so I won't need any circuits or modules relating to emissions equipment. It would be nice to have a reliable, modernized electrical system with capacity for future expansion.

I suck at electrical, but I know people who don't suck at electrical. I have a good set of Wirefy crimpers and adhesive shrink wrapped connectors.

Any advice?

 

[Pighead]

How feasible would it be to refurbish the OEM harness, remove or repurpose the unused circuits, replace the old glass tube fuse box with a modern spade fuse box, and add a relay box to accommodate future accessories like an air compressor, etc?

That sounds like a good idea. You can lose about half of the under-hood and under-dash wires to match the de-smog. I added a small fuse block before the stock fuse box and kept a lot of the original wiring but used the new fuses for accessories.

 

[charliemeyer007]

OEM harness from 1980 is like 45 years old already vs a 14 years old aftermarket. I have had my 72 since 82 and I think I have blown like 5 fuses. I have a cartridge box of spare fuses in the glove box.

It would seem to me sorting out your wiring would be safer/faster/easier option. What you have like 12 circuits, do one every Saturday and in 3 months its totally fixed.

It was hard to learn the if it ain't broke don't fix it rule. On the other hand stress is the greatest killer because it works on you even when you sleep so if you are really worried, health wise you should likely have someone else fix it.

 

[cruisermatt]

It sounds like you have it figured it out really - and I would take the same approach, minus replaceing the fuse block. The original glass fuse blocks are super reliable as long as they aren't modded or corroded. As far as future accesories you likely aren;t going to actually power them off the original dash wiring, so I would just add an auxiliary panel if you think you are going to have a lot of accessories.

If you remove the emissions computer circuits the original harness gets a lot more compact as well. It is very straightforward to completely remove that wiring and you only need to re-splice one or two wires if I remember correctly.

 

[Engineer8000]

Does the 80 MY have the crimped on fuse block? The large connectors on the rear of the earlier fuse panels were a source of bad connections. The green one would melt. I'm with @cruisermatt If the plating on the fuse terminals is still good, that should work for you. Also recommend the Toyota headlight relay upgrade to remove that high amp connection from the fuse box. The wiring that Toyota used in the main harness holds up quite well. I have only seen the ends exposed to heat get brittle. The connectors are readily available except the large green and black ones on the back of the early style.

 

[CruiserInProgress]

I did most of what you plan on my desmogged 79 oem harness, deleting unused circuits and adding a couple. You might want to check out that thread.

https://forum.ih8mud.com/threads/79-fj40-main-harness-deleting-unused-wiring.1357300/

First, I studied the schematics from Coolerman's site and labeled what I could in terms of known terminations to make the job less confusing.

Then, I pulled the oem harness from under the dash and unwrapping it, continuing onto unwrapping the harness in the engine compartment. Although many of the connectors required cleaning, the color-coded wiring under the tape was like new.

In your case, you'd be pulling the aftermarket Painless harness, so you may run into some mismatch on the terminals used for it vs the OEM. Coolerman has quite a few oem connectors if needed to straighten things up.

About your fuse block question, I replaced mine with an oem type, trying as best I could to match the oem schematic, wiring and wire colors. It works great and bolts into where it should in the driver foot well. Using standard wiring makes any future troubleshooting way easier. If you still have the original fuse block with large connectors, you're way ahead of the game.

 

[Engineer8000]

x2 what @CruiserInProgress said. This is one in progress for a local '72 40 owner, waiting for test fit.