Left Rear Blinker won’t work.

[BroncoJD21]

My current dilemma is that my drivers side rear blinker will not work when I turn them on. The fronts work perfect. However, when I turn the right blinkers on, both back blinkers turn on.

I’ve replaced bulbs, relays and the ground at the battery has been cleaned which got me this far. Originally none of the blinkers worked. The hazards work fine.

From what I’ve read it could be a grounding issue or a problem in the steering column with the switch.

I’ve seen that the lights need to be grounded but I’m not sure what to do. I can’t find photos to show me how to do it or what to get. I see a yellow and brown wire going into the top light. And a black one going into the reverse light below. There is one brown wire coming out of the connector that connects to the light. Is that what needs to be grounded?

Also my reverse light doesn’t work, but haven’t got that far yet.

Any help is appreciated.

 

[DirtDonk]

Brown wire is not a ground.
The tail light grounds through the bucket/reflector to the body via the mounting screws.
There are supposed to be two insulating pads over the screw holes so that the bucket doesn’t actually touch the body. The grounding occurs through the screw.

The two wires going into the upper tail lamp socket are for the two (or three if you prefer) different functions that are done through the one main bulb.
Those are the running lights, brake lights, and turn signals. Brakes and flashers and signals work through one filament, and tail lights / running lights work through the other.
The turn signal switch controls turn signal and brake lamps, so that is a common denominator here.

I believe the brown is the running light. Which seems to work since you say the tail lights work with the headlight switch. Correct?
The reverse light has its own ground wire that mounts to the body inside the light cavity.
This does not sound like a ground issue, even though it’s a strange one. I am leaning initially towards the turn signal switch, but can’t prove that in my mind just yet.

Manual transmission or automatic? That will dictate where the backup lamp switch resides.

Since both left and right bulbs light when you turn the right signal on, it could be some wires crossed, the turn signal switch, or perhaps back to a bad ground.
Make sure both taillights are grounded through their housings, and make sure that you are actually seeing the correct filament light up.
Obviously, the running lights are dimmer and the brake lights and turn signals are brighter. so make sure that those are working correctly or not.
It might be another clue.

 

[BroncoJD21]

Brown wire is not a ground.
The tail light grounds through the bucket/reflector to the body via the mounting screws.
There are supposed to be two insulating pads over the screw holes so that the bucket doesn’t actually touch the body. The grounding occurs through the screw.

The two wires going into the upper tail lamp socket are for the two (or three if you prefer) different functions that are done through the one main bulb.
Those are the running lights, brake lights, and turn signals. Brakes and flashers and signals work through one filament, and tail lights / running lights work through the other.
The turn signal switch controls turn signal and brake lamps, so that is a common denominator here.

I believe the brown is the running light. Which seems to work since you say the tail lights work with the headlight switch. Correct?
The reverse light has its own ground wire that mounts to the body inside the light cavity.
This does not sound like a ground issue, even though it’s a strange one. I am leaning initially towards the turn signal switch, but can’t prove that in my mind just yet.

Manual transmission or automatic? That will dictate where the backup lamp switch resides.

Since both left and right bulbs light when you turn the right signal on, it could be some wires crossed, the turn signal switch, or perhaps back to a bad ground.
Make sure both taillights are grounded through their housings, and make sure that you are actually seeing the correct filament light up.
Obviously, the running lights are dimmer and the brake lights and turn signals are brighter. so make sure that those are working correctly or not.
It might be another clue.

The running light is the one that is usually on side right? Mine doesn’t have those. It is an automatic.

 

[Broncobowsher]

Without any turn signal, do the brake lights work? Both of them.

There is also a chance that a hack wiring repair was done where the driver's side was wired into the passenger side.

 

[BroncoJD21]

Yes the brake lights work without the turn signal.

The wires look good as far as I can tell. Like they haven’t been messed with.

Do you have a link or pics of the insulating pads? I’m not sure those are there. It doesn’t have gaskets. Not sure that matters.

At one point, I would take off the hazard relay and all blinkers except the back left worked fine. I guess I can go get new bulbs for the back and see if that makes a difference. I’m sure it won’t.

I guess the problem is in the steering column. But everything seems to indicate not.

 

[DirtDonk]

The pads are not critical, so don’t worry about them too much at this point.

When using the word “running light“ I’m actually referring to the tail lights. So when the headlights and running lights are on, whether in the first or second position of the headlight switch, the tail lights should illuminate.
And yes, so should the side marker lights if you had them. But since you don’t, it’s a non-issue.
However, the tail lights and front turn signal lights do both duties.
So when you pull your headlight switch out to the first notch, both of your front signal lamps and both of your rear tail lamps should illuminate with the dim filament.

 

[DirtDonk]

And when things are working properly, your turn signal switch should reset the brake lights.
If you push on the brake pedal and both brake lights come on, turning the signal switch to the left or to the right should stop that side from working on the brake system, and they should blink.
If they don’t blink, they should at least go out.

Does this happen?

 

[BroncoJD21]

The pads are not critical, so don’t worry about them too much at this point.

When using the word “running light“ I’m actually referring to the tail lights. So when the headlights and running lights are on, whether in the first or second position of the headlight switch, the tail lights should illuminate.
And yes, so should the side marker lights if you had them. But since you don’t, it’s a non-issue.
However, the tail lights and front turn signal lights do both duties.
So when you pull your headlight switch out to the first notch, both of your front signal lamps and both of your rear tail lamps should illuminate with the dim filament.

Front signal and tail light illuminate on first notch.

 

[DirtDonk]

Thanks. And just for our information, in case it wasn’t already posted, what year is your bronco?
Doesn’t happen to be another 73 by any chance, does it?

 

[BroncoJD21]

1976

 

[DirtDonk]

Thanks. So is the wiring original? If so, then somebody removed the side marker lights at some point and may have left the wires and sockets laying around under the fenders.
Could be one of them has had a problem, but ultimately, I don’t think that’s what’s giving you a headache at this point. Might be though, so it never hurts to search out what the previous owners have done.
Since your truck definitely came with side marker lights from the factory, if it’s an original harness, then there are likely still wires somewhere and possibly bad cuts and splices.

 

[BroncoJD21]

The wiring looks original. The vehicle is wrapped, which I will eventually remove. Then I’ll be able to tell if the hole was patched but I don’t feel one at all. I thought about cut wires. Just odd that hazards work fine and that one is giving me trouble. I’m finding that electrical is fun.

 

[Hallboss]

Not to hi-jack this, but have similar brake/signal issues on the rear as well. Wiring harness is American Automotive all front/rear lights work, until I turn on the headlights. I'd say the brake lights and left/right signal when running lights are not on may be a little dim, but visible during daylight. Once I turn the headlights on you can just barely see the rear brake lights and turn signals activate... but it is not noticeable at all if not directly looking into the lens. The fronts work perfect with running lights on or off. I've removed and cleaned every ground contact I can find with no luck.

I don't have these insulating pads though... The tail light grounds through the bucket/reflector to the body via the mounting screws. There are supposed to be two insulating pads over the screw holes so that the bucket doesn’t actually touch the body. The grounding occurs through the screw.

I'm going to insulate the rear buckets today to see if that may help????

 

[DirtDonk]

That shouldn’t help in the electrical department.
It might be worth a try, but it’s probably not the issue. Having the tail light housing touch the body is actually just an additional ground if you look at it that way.
So it’s not hurting your light function that I can see.
Best to check other grounding.

 

[4xfun]

A couple of more items to check:

1. Is your license plate bulb coming on when you turn on your running lights? This is not going to be the solution, but it will help identify possible wiring issues.
2. Have you looked to see that the same filament is creating light on both sides. One filament is higher than the other and burns with a different intensity. This could indicate another wiring issues.
3. Are any of the bulbs LED? That can cause strange issues due to the flasher type, a lack of a resister, or the polarity of the bulb.
4. Do you have a trailer connection? The plug is a good place to check if the system is working before the tail lights. You can get a 4 wire plug tester for a couple of dollars,
5. I would track down the electrical wiring diagram for you model. It really does sounds like you have an issue with the wiring between the flasher. turn signal and hazard switch. Based on your responses, the wiring between the brakes and the appears bucket appears to be working, The problem you have is that the interruption that the turn signal and hazard switch create is not working properly.

 

[EPB72]

SeaBiscuit68

Here is diagrams ,, that another member here took the time to re draw and post for us ,, so thank him...

at this point I would go to the steering column/turn signal connector and do some testing, ,, you can send power down the circuits to rear right and left , this would give a dirction to go ,, either underdash / turn signal issue or the wiring from switch to rear lights... If you don;t already have a test light, multimeter, and a couple jumper leads, it maybe time to get them ...

 

[4xfun]

This may be stating the obvious, but you do know that there are two flasher relays. One is for the turn signal and the other is for the emergency hazard flashers.

 

[DirtDonk]

Has the body been repainted? Is it rusty,?
Are the tail light housings clean where the screws touch them? Are the screws clean!
Does your battery have a body ground in addition to the main engine ground?

And just to supplement that, since I have found this can be an issue on just about any old truck, Ford or Chevy, or Toyota or otherwise… If nothing else works, make yourself a ground jumper wire to attach between the frame and a piece of metal on the bed.

You can test the ground theory by running a jumper lead from the battery to the housing.
That’s a lot of wire to play with, so you could do it with a shorter one by finding any good grounding point on the frame or body and touching the other end to the tail light housing.
If the running lights get brighter, then you know it’s a ground issue.