Ford F530F Super-Duty

[Paintjar]

I am working on a 1990 Rockwood Driftwood 36'. Having problems with brake lights. It has a high middle light in the rear. The brake lights work with the turn signals, except for this one. It is not effected by the turn signals. An independent light. Is there a relay for this? How does this work and stay seperate from the turn signals. Anyone have wiring info on this. I am guessing that it would work the same with any system using the brake and turn signal combo type wireing. Thanks for reading and any help would be appreciated.

[WilleyB]

I do believe it's controlled by a logic module. I had to get one for my old 84 Buick. The electronic term for it is "AND gate" that is it takes two signals to turn it on. one from the right brake light circuit and one from the left brake light circuit. The only time there will be an output to the center light is when both brake lights are on.
Cheers
Willey

[Paintjar]

I think finding that would be like trying to locate a muffler bearing.

[WilleyB]

If I recall the one I bought it had 3 wires, was about 3" square and about 3/8" thick, was black molded plastic. Actually it could be anywhere but would have to be connected to both right and left brake lights and the center brake light. I'd look close to where the elect wiring harness at the rear separates to left and right sides.
BTW if it works, what are you trying to do with it? To the best of my knowledge it illegal to have the center light flashing that's why I had to get a module to stop it.
Cheers
Willey

[Nick-B]

Ummm, is this a trick question???

Sounds like a third center brake light that has been standard on cars since the mid 80's and all vehicles since the early 90's.

Factory wiring to that light would be separate from the rear turn/brake lights since you don't want it flashing with the turn signal . Some aftermarket center brake lights used a logic circuit (as WilleyB mentions) since the aftermarket add-on units normally did connect to the existing turn/brake wiring.

No muffler bearings involved.

[Paintjar]

OK, All sounds good. I traced the wire from the light. It is seperate from the brake lights. If I apply 12v to it the light comes on. From the switch at the brake pedal there are 3 wires. 1 wire is hot and places 12v to the other 2, one of which makes the brake lights come on and the other( I suspect) is for the center light. There must be an open somewhere or if it goes to a relay, that may be where the problem is. I started at the rear and began my trace of this single wire, as I get closer to the engine, it becomes very difficult. Starting from the brake pedal switch is even worse tracing. I am going to have to unwrap these harnesses to get this I think. Unless someone can tell me another way or where this relay or junction,fuse ,or block may be located on the frame. It may even use the same brake light relay, I don't know. It is hard to trace without being able to dissconnect what ever is there as the ohm readings are not correct. Thank you very much for your input in helping me troubleshoot this.