One brake light out only when headlights off

[robotzombies]

Hey everyone,

I have a bit of a brake light problem. The driver's side brake light is out; the problem is that it's only out when the headlights are off. Which means that it works perfectly fine when the headlights are on. The passenger side brake light works fine, whether the headlights are off or on. They also both work with the hazards on. Both turn signals work, as well.

The electrical diagrams doesn't say much, as it looks like there are a bunch of things shared with the brake that are shared for things that still work. The ground for the brake lights seem to be shared, so if one is working and one isn't, does that rule out the ground? Since it's only the one brake light, does that also rule out the headlight switch?

Any ideas? It's an '89 Bronco II.

 

[adsm08]

Did you check the bulb? The most likely cause is a burnt bulb with the filaments touching.

 

[robotzombies]

Did you check the bulb? The most likely cause is a burnt bulb with the filaments touching.

The original bulb looked brand new. However, I replaced both the bulb and the socket with no difference. The same brake light still doesn't work, but works with headlights on.

 

[jonathan62019]

Brake light? Or tail light? Get a tester and see id there is juice to the plug. If not its a wiring issue. And that does not seem fun to deal wth

 

[Spott]

I'd start by checking the grounds. If there's a bad ground, the returning electrical current will try to find other routes to complete the circuit, sometimes flowing through other bulbs or switches.

 

[Pauls 4x4]

I'd check for proper fit and function at the turn signal switch if all the other's fail. But the connectors on these things often fall apart.

The Brake lights route through it on the green/red wire from the switch up to it because it cuts the signal for the turn signal flash. Need power at white with blue and light blue (I think). The top connector often has the individual wire pins come loose and back off causing me intermittent headaches.

If you where by me I have a good OEM one I'd give you...

 

[jeremysdad]

Bad ground was my first thought. Steel connectors rust, sheet metal rusts, steel screw rusts...boom, random bad circuit.

Copper also rusts...it's green. Rust is oxidation, as well...just got its own name cause it happens quicker, I guess.

 

[robotzombies]

Thanks for the input, everyone. I still haven't fixed the problem, but that's because I ran out of daylight, so I was crawling around searching for the ground with a flashlight. Plus, it's all sorts of wet and rainy where I am.

So I will check again tomorrow. The electrical diagram says that the closest ground is somewhere between the left and right hand rear lights on the black wire, so that will be where I'm looking. I think it may be hidden by the gas tank skid plate, however. I took off the right hand light, but no dice for a ground.

I'll report back if I find it. Thanks again for the help everyone.

 

[robotzombies]

Honestly, I still can't find the ground for the lights. But it seems the culprit could very well be the multi function switch. The brake light seems to come on when the plug is played with. I will open up the shroud and clean it up. I think it should work better.