Only 1 brake light and blowing blinker fuse

[Laine D]

Unfortunately my lights are deciding to make sure I’m not bored during quarantine. The drivers side rear tail brake light will not come on when I hit the brakes. The bulb will aluminate perfectly fine with the running lights and the blinkers. I got a test light and tested the 3 wires going to the light fixture. The GREEN wire is for the brake lights, the BROWN is for running lights, they both will be used for the blinker. There’s also a ground. I found that the green wire will only have power when the blinker is on, not when I hit the brakes. I tried a new bulb and there was nothing, all my fuses are good as well. Since this has happened my blinker fuse won’t last more than 20 minutes of using them.

 

[gandalf]

I'd start with a new blinker control unit. It's hiding up under the dash somewhere. Other than that, it sounds as though you may have one of those dreaded electrical gremlins.

 

[Laine D]

I'd start with a new blinker control unit. It's hiding up under the dash somewhere. Other than that, it sounds as though you may have one of those dreaded electrical gremlins.

I hate the lights in this thing. The previous owners must’ve had their heads up....

 

[aggiediesel01]

Unfortunately my lights are deciding to make sure I’m not bored during quarantine. The drivers side rear tail brake light will not come on when I hit the brakes. The bulb will aluminate perfectly fine with the running lights and the blinkers. I got a test light and tested the 3 wires going to the light fixture. The GREEN wire is for the brake lights, the BROWN is for running lights, they both will be used for the blinker. There’s also a ground. I found that the green wire will only have power when the blinker is on, not when I hit the brakes. I tried a new bulb and there was nothing, all my fuses are good as well. Since this has happened my blinker fuse won’t last more than 20 minutes of using them.

Do you have tilt column? This is a classic symptom of the wires or contacts going bad in the turn signal switch under your steering wheel. Your blinker relay could be failing as well but it would affect both front and rear if so. It's located in your under dash fuse panel. Look for the round aluminum can looking thing that clicks when your working blinker is on. There's a second one around there that is for the hazards.

 

[aggiediesel01]

There's a full set of wiring diagrams online for the '84/'85 trucks somewhere. I posted a link to them recently but I can't remember where right now. They should be basically be the same for this function of yours.

 

[Laine D]

Do you have tilt column? This is a classic symptom of the wires or contacts going bad in the turn signal switch under your steering wheel. Your blinker relay could be failing as well but it would affect both front and rear if so. It's located in your under dash fuse panel. Look for the round aluminum can looking thing that clicks when your working blinker is on. There's a second one around there that is for the hazards.

Funny thing. I just bought a new clicker the other day. And I had the steering wheel off to check the blinker wiring a while back. The screws holding it down had come loose and it was grounding on the steering wheel. I thought that I fixed it, maybe not. I’ll check it out

 

[Scotty4]

http://www.garysgaragemahal.com/

If you rummage around on here you will find diagrams for everything Bullnose. I dont have any manuals later than this but they always pop up from someone on here

 

[Cubey]

Check your trailer wire harness under the bed too. I had no brake lights (or was it tail lights) when the factory T connector that taps into the rear lights to supply a 4 wire trailer connector had loose connections.

You can remove the T connector and directly plug in the two plug ends to see if that helps.

 

[Laine D]

Check your trailer wire harness under the bed too. I had no brake lights (or was it tail lights) when the factory T connector that taps into the rear lights to supply a 4 wire trailer connector had loose connections.

You can remove the T connector and directly plug in the two plug ends to see if that helps.

Are you talking about these?

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[Cubey]

Are you talking about these?

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It looks something like this.

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[Laine D]

It looks something like this.

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Yeah I have some other thing for the trailer lights. I traced the wires and found a bunch of scotch locks lol. Didn’t fix anything though. I’ll read the wiring diagrams tonight

 

[Cubey]

Yeah I have some other thing for the trailer lights. I traced the wires and found a bunch of scotch locks lol. Didn’t fix anything though. I’ll read the wiring diagrams tonight

My F250 had that factory slitter and plastic splicers, so it had 2 4-ways. I suspect the factory one was going bad for trailer use and they fixed it that way. Then it got so bad that it was messing with my rear lights working at all. I just removed the spliter, problem solved.

I had an ol Dodge 1 ton van that had rear light gremlins. I just ended up running new runs of wire to the lights, which fixed it.

 

[Laine D]

My F250 had that factory slitter and plastic splicers, so it had 2 4-ways. I suspect the factory one was going bad for trailer use and they fixed it that way. Then it got so bad that it was messing with my rear lights working at all. I just removed the spliter, problem solved.

I had an ol Dodge 1 ton van that had rear light gremlins. I just ended up running new runs of wire to the lights, which fixed it.

To be honest, I think even when I figure out this issue I’ll probably run new wire because there are a lot of pointless wires that the previous dude put in for only god knows why. Start fresh

 

[Laine D]

Funny thing. I just bought a new clicker the other day. And I had the steering wheel off to check the blinker wiring a while back. The screws holding it down had come loose and it was grounding on the steering wheel. I thought that I fixed it, maybe not. I’ll check it out

So after about 4 hours of messing around with the blinker mechanism, I found a lot of wires that were grounding against the steering shaft and it looks like whoever worked on this before me had put a plastic card underneath the mechanism to make it not ground properly. For whatever reason. So I ordered a new turn signal switch and I’m pretty sure that will fix my issues.

 

[franklin2]

I got a test light and tested the 3 wires going to the light fixture. The GREEN wire is for the brake lights, the BROWN is for running lights, they both will be used for the blinker. There’s also a ground.

You said you were going to study the diagrams, and hopefully your steering column work will fix the problem. In case you still have to do more troubleshooting, you are correct, the brown is for the running lights ONLY. The green wire is the brake light AND the turn light.

If you look at the diagrams, that is why the turnsignal switch looks so complex. When the lever is in the center, it directs the brake switch signal through to both rear taillights. When the lever is moved right or left, it lifts that certain bulb off the brake circuit, and puts it on the blinker circuit. The brake circuit and the turn circuits use the same wiring to the rear and the same bulb filaments in the rear.