Tail Light Issues

[JaxLax]

Sometimes it's easiest to write it all out so I can see it in front of me.

I'm having issues with the rear tail lights and want to see if anyone here has some thoughts or maybe had a similar issue.

Things that work:
Running Lights and Brake Lights - so I know it's not a bulb/power issue
The Hazard flash works for a few repetitions then fades/goes solid

Things that don't:
either of the turn signals. When I try LEFT - I get nothing. When I try RIGHT - I get both flash (hazard style).
Rear backup lights (I know they are on a different switch, but still gonna mention)

Doesn't make any sense to me. I know the hazard flasher is a separate switch from the regular turn signal; so I should start by replacing/testing my standard turn flasher?
But why then does right turn = flashers? Power is somehow present unless they've crossed those wires?

I know it's got a tapped trailer wiring in the rear; maybe they removed a ground or tapped it incorrectly? It's on the plan to remove the tapped harness, but I need to find time to do it slowly. Plus the A/C unit on the tunnel cover means that the dash wiring is even more of a rats nest than normal [along with it's numerous taps and abandoned leads].

Would I just be better off getting a new turn flasher unit and running fresh and bypassing all this? I will eventually rewire the whole vehicle in a few years when I break it down, but I want to at least have general functions for now.

Thanks in advance for any thoughts or help!

 

[Slowleak]

I would start by cleaning all the rear grounds. Make sure you have a good flasher unit. Either replace it or use the one from the hazards. Then, with a meter or test light, start checking power in the rear harness and trace it back to the column. On my 77 there is a plug in the harness on the drivers side of the rear tank by the frame. You can unplug it and check for power there.

Turn signal power flows thru the hazard switch to the turn signal switch in the column. You could have a bad switch, or a short in the rear wiring. Sounds more like a short to me..... I had a pinched wiring harness once after replaced a rear tank. It caused similar issues.

The reverse light issue is probably your backup switch. That’s a pretty simple circuit.

 

[Apache Bronco]

I just got done cleaning up my wiring too. Sorry, but you have to start at the taillights and work your way back. Remove & replace all bulbs, check sockets. Repair all wiring. Check all connections. Mine was wired for flat tow and had a trailer brake - real mess. Scotchloks suck!

 

[mpboxer]

Mine had a wiring harness for a trailer in the rear also. I eliminated that and verified grounds especially in the taillight housings. For the reverse lights, traced down the simple circuit Slowleak mentioned. I thought my NSS switch at the C4 was bad, so I bought a new one. Thought the new one didn't work either, but turns out all I needed to do was loosen the bolts holding it to the tranny and move it a bit in the slotted holes.

 

[DirtDonk]

Sounds like the hazard flasher unit is going bad. The fact that it works for a moment or so and then just goes solid says something.

Of course it could still be in the turn signal switch, but that would be my last choice of things to do. Like the others said do the other stuff first.
I would concentrate on, and put that trailer splice at least near the top of the list. They're often the culprit in older trucks like this.

Don't ignore the front turn lamps either though. Something up there could be putting a larger load on the hazard circuit and causing the flasher unit some grief.

Is this the 77?

Good luck.

Paul

 

[JaxLax]

Is this the 77?

Yup, only one I've got.
Just keep looking ahead to the next project or at least the next thing I can do at night when the kids are asleep.

The pitman arm and pump are daylight/longer projects. I can pull the trailer wiring and trace stuff in the garage and still fire it up on the way to work the next morning if I don't complete the project.

 

[Skiddy]

I would start by cleaning all the rear grounds. Make sure you have a good flasher unit. Either replace it or use the one from the hazards. Then, with a meter or test light, start checking power in the rear harness and trace it back to the column. On my 77 there is a plug in the harness on the drivers side of the rear tank by the frame. You can unplug it and check for power there.

Turn signal power flows thru the hazard switch to the turn signal switch in the column. You could have a bad switch, or a short in the rear wiring. Sounds more like a short to me..... I had a pinched wiring harness once after replaced a rear tank. It caused similar issues.

The reverse light issue is probably your backup switch. That’s a pretty simple circuit.

my 74 has the plug back there as well. when my rears were acting goofy found some wires melted together next to the muffler

 

[Slowleak]

my 74 has the plug back there as well. when my rears were acting goofy found some wires melted together next to the muffler

That’s a bad spot back there.... Mine were all boogered up too. I tucked and tied them away with some cable ties.

 

[Rustytruck]

Don't ignore the front turn lamps either though. Something up there could be putting a larger load on the hazard circuit and causing the flasher unit some grief.

Is this the 77?

Good luck.

Paul

I agree with this. Check the grounds for the front lamps. At one time I was chasing the rear lights and had issues with the rear housings. The assembly had loose rivets and poor grounding. All flashers are not created equal. There are heavy duty units you use when you tow trailers because of the extra lights and in some cases different units for LED swaps. On my 1974 at the rear pigtail disconnect drivers side by rear gas tank there is a separate ground eyelet to the frame. Make sure you have a good ground from the negative post on the battery to the body.

There are weird things with lighting circuits and bad grounds. If there is a bad local ground sometimes the lighting back feeds for grounds through another light bulb on the same circuit especially if there is a trailer plugged in.

 

[JaxLax]

Back into this part again.

Removed the trailer harness and double checked down all the wires for frays or other issues. None found there.

But the same problems still occur and now I can see where there's a yellow jumper from the passenger to the drivers side that looks to be causing/creating the double flash on right turn.

Each and every side though has been tapped/taped/cut/spliced. Thinking that the bets solution might be to follow everything back until I have a few inches of stock harness and cut everything out from there. Then rewire it all fresh from that spot correctly?

I feel like a vendor makes a rear harness section. Anyone know of it specifically? Sometimes I think it's easier to rip it out and start over rather than chase little bug by leprechaun.

I will rewire when I do the real restoration, so I'm not too worried about having to keep the stock colors or routing. I just really want to have working turn signals (and rear lights).

I know all the bulbs are working and such, I know the flashers work, etc etc etc.

I've got some pictures for Monday. Can't do anything with them right now since I don't have a cord.

 

[Gwunited2]

I will post a picture of how I reworked the back half of my Bronco with a trailer wire harness and Weatherpak waterproof connectors. Solved my issues and was inexpensive.

 

[DirtDonk]

...I feel like a vendor makes a rear harness section. Anyone know of it specifically?

Looks like what you might need: https://shop.broncograveyard.com/Chassis-And-Taillight-Harness-1968-77/productinfo/18042/

Paul

 

[JaxLax]

Looks like what you might need: https://shop.broncograveyard.com/Chassis-And-Taillight-Harness-1968-77/productinfo/18042/

Paul

Paul,

I came back across it after searching, but looks like I may have a few offers for donor harnesses/sections from members. Hopefully I can snag one from mid-bronco to sockets complete.