Weird tail light and rear marker issue.

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Gippster

Gippster

Joined
May 30, 2024
Threads
17
Messages
107
Location
Colorado
I'm trying to figure out what's going on with the 1984 FJ60. Here's the breakdown:

ComponentStatus
Headlights✅ Working
Brake Lights✅ Working
Dash Illumination✅ Working
Front Side Markers✅ Working
Rear Side Markers❌ Not Working
Tail Lights (Rear)❌ Not Working
License Plate Lights❌ Not Working
Rear left turn signal✅ Working
Rear right turn signal❌ Not Working

I've replaced all the fuses. I thought maybe it was the fusible link, and so I replaced that with the one Cruiser Trash sells. Light bulbs are good, wiring is in OK shape. Oddly enough, it worked a couple of nights ago and decided to crap out today.

Any suggestions?
 
Have you taken a look at the truck wiring diagram and traced the harness? The rear light wires (all the ones that seem broken) pass through a few different big combo connectors in the rear drivers quarter panel and maybe some of the connectors or pins are loose or corroded. Were any of the fuses blown?
 
CruiserTrash said:
Thank for buy my kit! Were the issues before or after you installed it?
Click to expand...

This issue occurred before the installation; after I installed the kit, the brake lights and the left rear turn signal began to function correctly.

PBcuiser said:
Have you taken a look at the truck wiring diagram and traced the harness? The rear light wires (all the ones that seem broken) pass through a few different big combo connectors in the rear drivers quarter panel and maybe some of the connectors or pins are loose or corroded. Were any of the fuses blown?
Click to expand...

I haven't looked at the wiring diagram(s) or the harness; not all of them are broken, which makes it especially odd to me, but I'll start tracing them. No fuses were blown, but I replaced them all anyway.

dmjay said:
Check that rear earth point under the tail gate.
My money is on a bad earth.
Click to expand...

I'm not familiar. Where would that be, so I have a general sense.
 
I second what @dmjay says about the ground point under the tailgate. It's hard to see, lay on your back and slide yourself under the truck. Look up at the bottom of the floor pan, and follow it all the way to the back right in the middle . There's a wire with a ring terminal connected to the body with a bolt. Clean all of that up and make sure the ring terminal is going to have good metal-on-metal contact with the body.

Check the area @PBcuiser mentioned - the left side, behind the cargo panel. Several connectors there that feed the rear electrics. They tend to corrode especially if you have even the smallest rust hole in the rear wheel wells (water will enter there). On early through 1984 or 1985 trucks all of the rear wiring runs on that side, but for 1985 and up trucks there's also wiring running behind the right side (passenger for US trucks) cargo panel. On my previous 60 those wires were disintegrating on me from corrosion and I had to rebuild a bunch of the harness.

Also, note that with my Fusible Link Replacement Kit, not only does the larger alternator charge wire from the kit have to go to the post on the back of the alternator, but the existing white charge wire has to stay on the post as well. You end up with both wires attached to the post via ring terminals and secured with the nut that lives on the post. That factory white wire feeds the cabin fuse panel. If it's left off the truck will run and the headlights will work, but most everything else will not work.
 
Yup, all wires, including the fusible link, are connected to the B post on the alternator. I did not deviate from what was already there! I'll run through the other suggestions! Sounds like a fun downtime project, will post updates.
 
Here's where I stand:
  1. Rear blinker works
  2. Rear brake light works
  3. Rear markers and tail (middle one) do not work
Investigating it:
  1. Opened the quarter panel, examined the connection, which looks fine for a 40-year-old wiring system. The intact, unburnt metal connections are all fine.
  2. Used a voltmeter to test the blue connector in the quarter panel, but found nothing. However, when the blinker is active, I get current on at least one of the connections.
  3. Went to the fuse panel, pulled the tail fuse out, and tested it; nothing.
  4. The relay controls click when I turn on the markers and headlight, and they seem OK.
  5. Edit: checked the tail ground, connected to the body, wire, and loop intact.
I'm now going beyond my knowledge base. Any other suggestions?
 
Last edited:
Stripped the ground wire, used the good old screwdriver against bare metal test, works.

IMG_859E9513-7D65-4B24-B72D-C34C24ABD0F7.webp

I then started to move up toward the cabin, tested the fuse, 12v, no problem, was looking under the driver side, and look at what I found:
IMG_2430.webp

That looks like a corroded wire harness for sure. How do I get to it from the driver's floor?

IMG_2429.webp
 
If you pull off the drivers side door “kick” plates, and pull up the carpet, you should see the loom run right along the edge there. Nice detective work!
 
@Gippster I'm not sure where that photo under driver's side is taken, but PB is right, the harness runs under the door sills. Take off those scuff plates on the sills and pull up the carpet. The carpet has a U-shaped plastic channel underneath the edge that the harness lives inside.

Wherever that photo is from, you're definitely looking at the imprint of wires that got HOT. My question is why didn't the fuse blow? Are you using Amazon fuses by chance? There's at least one story here on Mud of a cheapo fuse not tripping and causing a smoke show. Always buy name brand fuses - for a small cost increase you get reputable safety from a reputable company. I like Littelfuse because they provide data and documentation on testing in their product datasheets. Not saying that's the issue for sure, just a guess at this point.
 
Yup, Amazon, went and got the good quality stuff. These wires were cut right off, so shorting wasn’t happening because the sleeve was preventing the copper from exposure. What a carnage.

IMG_2442.webp


IMG_2445.webp
 
Aaaaaaannd fixed! Patched them up, connected, I have tail lights. That was totally so much fun. Now I have to wait for new tail light assembly to arrive.

IMG_2446.webp
 
So several of those wires were just hacked off and left wide open??? Was your truck missing a fuse when you got it - maybe the previous owner pulled the fuse that fed those wires.

Take a look at the color codes in the wiring diagram and see what they’re for!
 
My theory is that this happened when the frame and undercarriage were sandblasted. It was missing fuses, but I doubt that was related to this. It’s old, it’ll have problems, none that I can’t seem to fix so far.

I never caught it up until I decided to mess around with the electrical. Didn’t have an excuse, rig was at Cruisers and Company for a while.

I have plans to eventually have The Rust Doctor do body and paint work, that’s when the holes get repaired.

Definitely was fun to troubleshoot! Now I have to put it back together, so I can go enjoy driving it.
 
I had a similar issue , and if I can suggest another thing to check : the splices in the rear harness that goes left to right of the cab. When they oxyde they break and cause the same problem. I had brake lights and turn signals but no positions.

sorry for the tread resurrection but i felt like it could help
 
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