Third Brake Light Is Possessed!!!!!!

[justwufn]

My third brake light seems like it has a mind of it's own. Sometimes it works and sometimes it does not. I went to get truck inspected & it did not pass the North Carolina state inspection. I read a lot of the previous posts and I sure hate the thought of shelling out $300 to fix the problem. I was wondering if there is a contact switch attached to brake pedal that is going bad that could be causing the problem to appear and disappear for no apparent reason.

Any suggestions would be appreciated.

 

[dogfriend]

There is a switch that controls the brake lights (and other things too) called the BOO (brake on/off) switch. It is possible that you have a problem with this switch.

Do the other brake lights come on? If the brake lights in the taillights work, but the third brake light doesn't, then it doesn't seem like the switch would be a likely suspect.

It might be worth it just to replace the switch anyway assuming it isn't too expensive (junkyard?)

 

[Alec]

Yup, if it's acting up independently then its not the brake switch. It's probably either a loose connection or bad ballast.

 

[justwufn]

The other two rear brake lights seem to work just fine, so I guess the ballast may be the problem.

Does anyone know if I have to disassemble the rear door to test the ballast or is there an easier route to determine ballast or lamp?

 

[dogfriend]

I looked through the diagnostic routine for having the 3rd brake light out. Basically they check all of the wiring and the BOO switch first, if it isn't any of that then they tell you to replace the 3rd brake light.

Make sure to verify that Fuse #2 is ok - it feeds the 3rd brake light only. Even if it looks ok, you may want to replace it anyway or a least verify it with a test light or ohmmeter.

This schematic is for 97 but should be similar to yours

 

[justwufn]

Well, I took the fuse out and cleaned it off and re-inserted it and bingo my third brake light works now.

I would highly suggest that any of you who are having an intermittent problem try this fix before you do any other repairs.

Not sure exactly why this fixed the problem, but the light works fine and it passed the NC state inspection.

Thanks dogfriend for your help in resolving the problem.



Johnny