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Discussion Starter · #1 ·
I have a 1989 Trans Am brake lights do not work third light in spoiler does work. I have power after break switch but no power at light socket any help would be great thank you
 

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I’m not very familiar with 3rd gens but do you have turn signals by chance. Rear specifically. Possibly front working but not rear. If so could be the signal switch in the column. That’s also assuming your signals and brake lamps share the same bulb. I know at some point some of those cars had amber signals out back but I forget when. So if your brake light and turn signals don’t work but the third one does I’d start at the turn signal switch. The reason is, since the third brake light works you know you get power past the brake light switch on the pedal. But power for the two main lamps has to pass through the turn signal switch before it goes to the rear lights. That way when your foot is on the brakes and you flip on, say your left signal, the steady brake lamp power is “overridden” (interrupted might be a better word) and the intermittent power to make the left lamp flash takes over. Does that make sense?
 

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It still could be that switch. It may be functioning correctly with respect to the turn signals and not with regard to the brake lights.
 

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Maybe you lost the ground back there and the 3rd brake light has it's own. Do you have an amp in the trunk by any chance? How did you test power at the socket, volt-meter across positive and ground at the socket, or positive at the socket to "any (chassis) ground"? That makes a diagnostic difference. I don't do 3rd gen either, but much of the 4th gen is carried over from the 3rd. I can see the tail light harness ground being one of those things. If it is, when you remove the carpet covering the trunk latch mechanism, you'll see the ground point attached to the wall the mechanism is on. Make sure that connection is corrosion free and tight.

Had a cracked tail light lense in the past? ...or any seperation between the body and lenses? If so, the sockets themselves could be very corroded. Everything may appear fine, but the copper wiring or sockets could be corroded and oxidized to the point power simply can't push past the resistance, its just as bad as an "open circuit". Mine got so bad 12" of copper had to be cut from every wire in the harness to get back to clean copper for the new sockets which came with 18-24" of new wire attached.

I had crazy tail light issues that made no sense. Spent years trying to get my tail lamps sorted. One day on a whim I ordered all new sockets because a light was seized in one. The sockets themselves appeared "good for their age" with that one exception. ...the copper hidden inside pristine shiny new looking sheathing was another story. The grounded copper was the color of Lady Liberty herself. GREEN! The positives copper was black. New sockets, clean copper, and not only did my tail lights work as designed, they were much brighter than the previous 12 years AND my fuel gauge came back to life AND read accurately. It "failed" by reading higher than actual until a year or so later when it was always past full. I was told by many that it was the sender in the fuel tank. Expensive and laborious repair even if done personally. I drove by mileage for several years and I'm glad I did. I might not love my car if I went through all of the effort and expense of replacing the sending unit and fuel pump only to discover it was all-for-nothing.

Clean copper AND good grounding back there makes a world of difference.

If you measured from socket positive to any chassis ground point, you skipped over the ground that actually completes the circuit through the lamp itself. If you measured voltage across both wires at the socket, and saw full voltage and amperage, that's a head scratcher.

I'm leaning on grounding. Either bad harness ground point (corroded) or bad (corroded/oxidized) wiring.

Sea Dog's explanation of the turn signals tie-in to the brake circuit suggests to me that the 3rd brake light is on its own in a manner of speaking, and that has me leaning harder on my theory.

Good luck man, I couldn't make sense of my issue either, and it was literally dumb luck stumbling onto my cause and solution. Hope you get this straightened out soon, and with minimal effort.
 

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His rear turn signals work though which would mean those grounds would have to be intact since the same lamp (bulbs) act as signal and brake light right?
 

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Discussion Starter · #7 ·
The car has only 30,000 miles on And has always been stored inside the wires and socko look to be in good condition
I removed the turn signal switch and can not find a new one. It has 4 pins and 2 little fuse looking things on it
 

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Discussion Starter · #8 ·
His rear turn signals work though which would mean those grounds would have to be intact since the same lamp (bulbs) act as signal and brake light right?
I found my problem the green wire and white wire at the turn signal switch have a short of some kind not making good contact
 
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