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Discussion Starter #1
The culprit is the driver side brake light. Turn signals all work, and parking lights work. But the driver's side brake light doesn't work when the pedal is depressed or flashers are engaged. I've chased this problem before in the past, I put in new flashers for the turn and emergency signals; as well as a new turn signal switch (maybe a yr or two ago). I just had the car in for some work and when it came back I noticed the light was out. They had to remove the center console and that shifts some wires under the dash around a bit. A few months ago I had this issue, but I went to the 10 pin connector fiddled with it a bit and the light came back. The male side of the connector is new (from the turn signal replacement), but the female side is old - I figured it was a loose connection at the pins.

So I went back to the well hoping to get some success but nothing brought it back to life. Alright electrical gurus, where should I start on this one?
 

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Start at the source, depress the pedal and use a multimeter to check for 12 volts at every connection point til ya find it.
 

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I'd check at the connection to the tail light harness at drivers side kick panel, then the turn signal switch. Suspect it's there.

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Discussion Starter #4
Start at the source, depress the pedal and use a multimeter to check for 12 volts at every connection point til ya find it.
I mean... I get the concept, but that doesn't narrow it down at all. Assuming I don't know every connection point between the TS switch and the tail light...for a hobbyist like myself, that's like saying, "check every wire."

I'd check at the connection to the tail light harness at drivers side kick panel, then the turn signal switch. Suspect it's there.
Ah, I didn't know about a connection in the kick panel! Any particular connection point or wire color I should check in the turn signal switch?
 

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I mean... I get the concept, but that doesn't narrow it down at all...
I wasn't trying to be smug, and I'm still not, but Google Images is your friend unless you obtain a Mustang wiring diagram. They're very simple, handy and affordable. Most of us don't know right off the top of our heads which wire is what on your car, and after 50+ years, people change wiring or replace it altogether. That sometimes creates new problems. I hope you find the answer quickly.
 

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Assuming your wiring is still pretty much stock this should give you an idea what wire goes where:

And here's the general path:

The thing is though, the turn signal and the brake use the same wire to the same filament in the same bulb. If the driver's side turn signal works it shouldn't be the wiring or the bulb. If the passenger side brake and flasher work fine,that means the power feeds from both are good so then the problem has to be in the switch.

I'd try fiddling with the hazard button. If that doesn't do it I think you're going to have to dig into the column to figure out what's wrong.
 

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Most wiring issues with these old cars are bad grounds. Check all of them around the tail light bucket as well as the bulb holders.
 
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Discussion Starter #8
I wasn't trying to be smug, and I'm still not...
Appreciate it, mate. And I understand - thanks for taking the time to chime in too! This has just been frustrating... -__-

...so then the problem has to be in the switch.
Yeah, it's mostly stock and original wiring. Looking at diagrams I figured that since 1 function worked that it had to be somewhere I was looking. I looked up some other info on the TS switch after reading your post and I think I have some places to look now. I didn't think it would affect the brake lights so I hadn't ever looked there. Thanks!
 

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The turn signal and the brake light both use the same filament in the bulb. Since the turn signal works the problem is not the bulb, the wire or the ground. It's the turn signal switch. It looks like you are going to be replacing it again. The cheap TSSs sold by the Mustang parts stores and the auto parts stores are junk.
Look at this- made by the original supplier to Ford.
Ford Turn Signal Switch - C7ZZ-13341-F - C&G Ford Parts (for non-tilt wheel)
Ford Turn Signal Switch - C7ZZ-13341-E - C&G Ford Parts (for tilt wheel)
 

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Discussion Starter #10
The turn signal and the brake light both use the same filament in the bulb. Since the turn signal works the problem is not the bulb, the wire or the ground. It's the turn signal switch. It looks like you are going to be replacing it again. The cheap TSSs sold by the Mustang parts stores and the auto parts stores are junk.
Look at this- made by the original supplier to Ford.
Ford Turn Signal Switch - C7ZZ-13341-F - C&G Ford Parts (for non-tilt wheel)
Ford Turn Signal Switch - C7ZZ-13341-E - C&G Ford Parts (for tilt wheel)
That was the issue, I worked on the switch a little bit and the tabs behind the cam were just a little loose. I got it fixed but when I put the switch back in I think a wire in the column got snagged and it shorted out and melted a couple wires. I've got the harness apart to repaid it now and all looks to be in okay condition. But I just ordered you link. Thanks a bunch, hopefully this next pass will have 100% less fire! x_x
 
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