Electrical Woes on 1969 FJ40

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May 7, 2019
Grand Rapids, MI
Hi y'all,

Meant to do a welcome thread, but have been consumed troubleshooting electrical gremlins. I just acquired a 69 FJ40V in relatively good condition, however I've experienced some 'changing' problems related to the turn signals.

When I got the vehicle, I noticed that the FR and RL turn signals worked, but only when holding the turn stick all the way down (for left) or up (for right). The RR and and FL signals do not flash. All lamps will light, and still do.

I'd been seeing some inconsistent behavior, like the fuel meter would not work all the time and the wipers basically flying off the windshield some times they were engaged.

Something else that changed during the troubleshooting run was that whenever the turn stick was moved fully up or down, both the FR and RL turn signals would flash (but never the other two).

I noticed the FR signal lamp was less bright, and suspected bad ground. Began hunting for some problems and corrected a bad splice. No change. I was looking the distribution block in the front right of engine compartment and checked voltage on the wires coming from the FR turn signal. ~11.5v on one side, 0v on the other. I moved the return wire up a screw and have full bright.

In the midst of all this wire jiggling and trying to see how things should be laid out and how to test, other components have gone inoperable - most importantly the brake lights (lamps are lit, but no effect from brake pedal).

The signal flasher is not making as pronounced a 'click' at this point, and since the previously working indicators won't flash I'm thinking I'll just grab a replacement flasher from NAPA to see if that improves any ops.

So currently, I have the following situations:

  • Headlights
  • Running lights
  • RL turn signal
  • Speedometer backlight
  • Occasionally, the passenger side turn signal lamp in dash is lit when holding stick up
  • Occasionally, the FD indicator lamp is lit
  • Interior 'room' lamp
  • License plate holder lamp
  • Brake lights (lamps work, do not 'flash' when pedal is pressed)
  • FL, FR, RR turn signals (lamps work, do not 'flash')
  • Reverse light
  • Hazards (switch does nothing)
I'm going to take another run through as I learn the wiring diagrams but looking for some advice on best troubleshooting path/order or any tips based on my description of problems?

Still a little fuzzy on the right procedure and places to check for bad grounds. If there's a 101-level thread for electrical troubleshooting I'd appreciate any pointers.

EDIT: Should mention I checked fuse bank under dash, cleaned all contacts and replaced with known good (tested) fuses at correct amperage. Have found BLUE/RED wire that came off the wiper fuse and it's clean severed. Will be tracking that down to see if it was a jumper or something that should be connected elsewhere.

Thanks guys!
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If your truck is anything like my truck, you're in for a frustrating experience. I hate electrical work (especially when it's cobbled), but I have a pretty good mind for it. Even so, it took me three solid weekends to get all my lights functional. Many of the lights on these trucks use the light housing to achieve ground. This tends to be a point of failure, so be sure each light has a good ground. My truck has had a couple previous owners and it seems like each one has had a go at the electrical system. I have inline fuses in strange locations, splices where the wire color completely changes, unsealed crimp connectors, wires just cut off randomly, and all sort of other maladies.

I've decided that the only real solution is to rewire the whole truck. I've been carefully going through the truck and documenting the electrical components so that I can draw up a new wiring diagram. There are some other components I want to add (HAM and CB radios, multiple USB charging ports, auxiliary lights, air compressor, etc.) so I'll include those in my wiring diagram and leave a little room for future expansion. This way I'll be able to plan out the system and do it right once and for all.
Thanks guys, I have taken front signals off and looks like I have good metal contact. Will order the turn signal arm and swap out the flashers to eliminate any faulty parts. For each turn signal I have 2 wires coming in from light housing through body and to a junction or distribution block. I assume the bolts on either end of the block provide grounding for all connections? Are these routed in any way (is position important)?
I assume the bolts on either end of the block provide grounding for all connections?

My truck is a '77 so I may have a different setup than what you have. My front fender-mounted turn signals each have three bulbs: one forward-facing running light behind a clear diffuser, one forward-facing turn signal light behind an amber diffuser, and one side-facing running light behind an amber diffuser. Two wires come into the turn signal housing. Inside the housing, one of the wires is spliced into two wires. From that splice, one wire goes to each of the running lights. The other wire that comes into the signal housing goes to the turn signal light. The reflectors inside the housing are made of metal and provide the ground for all three bulbs. The circuit path is wire > bulb > reflector > ground wire > housing mount bolt > ground.
Does your truck have a hazard switch?
Does your truck have a hazard switch?
Oops, I see that you mentioned your hazard was inoperable. Sorry.

I can help you trace out some of these circuits over the phone on Friday. I've done a lot of wiring repairs on FJ40s at this point... I would guess that you don't need to do a full re-wire on the truck if the original harness is intact.
I would guess that you don't need to do a full re-wire on the truck if the original harness is intact.

It's rare that you NEED to do a full re-wire, but then you start thinking about how happy you'll be when the wiring isn't a cobbled mess and it turns out that you really WANT to do a full re-wire. It's an investment in your mental health!
Have replaced both flashers and no change. Loss of brake light function is my primary issue right now - does the inline fuse for hazards (under the cowl vent) figure in the equation?
Update: inline fuse for hazard burnt, exploded and melted fuse holder. Replacing that now!
If the fuse blew, don’t replace it with another one yet... you’ve got a short somewhere.
I spent a few weekends on my 69 to get the electrical all working. Schematics will help a lot— impossible to get it resolved without them. Trial and error and patience will serve you well for this project. Most issues relate to bad grounds. I ran a jumper ground for the license plate light and rewired a couple of other lights. Brake lights were the biggest pain— lots of trial and error. Good luck.
Last night I learned that what seems like a system of related problems can really just be a bunch of small, totally separate issues. I made some progress in a few areas.

Hazards are now working via dash switch. The fix was pulling that inline fuse (it was melted), replacing the fuse holder with a proper soldered splice and then wrapping the nearby bracket (holding the wire loom) that had corroded, broken and cut into that circuit (probably what caused the short).

Also found some strange OP wiring for the front turn signals. The FL signal had the solid green wire to GROUND (what??!?) and once I moved that to the wiring block it lit right up. I have a larger issue revolving around the turn signals and brake lights so I will post a new thread on that.

In the course of my troubleshooting I discovered that the wipers and fuel gauge had stopped working. The fix for the wipers was pulling the fuse from the panel (again), using a nice cocktail of barkeepers friend and water to abrade the contacts and then reload fuse. Bam - started working. I will pull the fuse panel and give it a strong cleaning all over (or replace if I can pick one up cheap).

Fuel gauge mystery was solved by jiggling the ignition switch, which also causes the FD light on dash to go into working state. Looks like I need to get into that and clean it up and tighten.

My plan for tonight is to pull all lamps, clean grounds really well and reseat, check the bulbs and go from there.

Thanks all for the advice. I will post some new threads specific to each ongoing issue and reference this one, hopefully that makes it easier for future searches.
If you think it's going to be a long term thing, you might consider starting a build thread. It'll centralize all your posts and allow people to see the history of where you started and what has been done. Plus, build threads are really fun to read.

I noticed that you're from Grand Rapids. I'm originally from Hastings. I'm hoping my 40 will be capable of cross-country road trips to visit friends and family in the next year or so.
Important for you to determine month/year of your truck. you can do this with the serial number and visit SOR.com to determine. From experience, mine is a 12/68 titled as a 69, the wiring follows the 68 model which is different than the 69. Also if you are looking for a good source for information, connectors, and electrical parts no better than Coolerman on this forum. Also look at his fusible link he sells, which if your truck doesn't have one you need to install it to protect all of your hard work. I grew up in Grand Rapids.
btw welcome to the forum, we love pictures of 40s :flipoff2:
Time for an update! Thanks to all for the suggestions. I have resolved many of the problems I was seeing. I learned a valuable lesson - never trust PO wiring.

Some specifics:
Horn not working - turns out I must have breathed near the connector to the horn in engine compartment. Just pushed it in and now the horn works (also identified I am missing the driver side horn).

Brake lights - isolated the issue to turn signal switch. The arm is very ‘wobbly’ and after running my fingers along all bullet connectors and securing I wound up putting some pressure on the column and brake lights started working. I will pull it this weekend and have a replacement on the way.

Turn signals - FR, FL and RR all work. The RL will flash only once when arm is moved, so I traced the wiring back checking resistance and voltage out to lamp. It all seems solid, so assuming this will also be resolved by new turn signal switch. Voltage levels are also now even and lamps bright to same level. I wound up disconnecting all wiring up front from the blocks, and just doing it myself making sure that the circuits were correct per wiring diagram.

Hazards - resolved by replacing burnt out inline fuse under cowl.

On to reverse, license plate frame and interior lighting!
Here’s a couple pics of my 40!
Ran into similar on my wife’s 40. @Coolerman has wiring diagrams for the 40s. Very helpful. Grounds were key for me. Also, take some time to refresh the fuse block. I took each fuse out and took a small wire brush/ steel wool to it. Sometimes the fuse block gets corroded.

Very cool truck!!!

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