Questionwe have a 65 mustang 6 cyl the brake lights just quick working the tail lights and turn signals work but but no brake lights I do not have a wiring diagram and do not know where the common grounds are for the lights can you help
AnswerSince your turn signals work, and they use the same wires and bulb filaments as the brake lights, we know it is not a problem with grounds, or wiring, or bulbs. There are a bunch of other things to check. First is the fuse - does your interior "dome" light work, and the dash lights? If so, your fuse is OK.
Second is the brake light switch - it may be under the hood, on the hydraulic line near the brake master cylinder, or it may be on the pedal mechanism up under the dash (there were two types in 65).
First look under the hood: Take a flashlight and look near the brake master cylinder on the firewall. There is a mushroom shaped switch, screwed into the hydraulic plumbing fitting that also holds the steel brake line, about 1 inch in diameter, with two wires going to it. Disconnect those two wires and then hold them together, with the metal ends touching, while someone watches your brake lights. If this makes them come on, you've found your problem - a bad brake light switch. If it doesn't make them come on, turn on your ignition as if to run the engine (you don't have to start it, just turn the key on), and try the same test again. If now they come on, it is still your brake light switch that has failed. To replace it, get a new one from NAPA and the special socket that fits them, just unscrew it and quickly replace it with the new one. If you do it quickly, you'll only lose a few drops of brake fluid (don't get it on the PAINT!) and you won't have to bleed the brakes. They only cost a few dollars, the special tool will cost more.
If you don't see the switch under the hood, it is under the dash, where the brake pedal lever pushes a button to turn on the brake lights when you move the pedal down a short distance. You will have to crawl under there with a flashlight and work the pedal up and down while you watch to see the switch and the plunger that gets moved when you just start to push the brake pedal down. That switch may be out of adjustment - but it also may not be working at all. It has two wires on it. Disconnect the wires and connect them together, metal ends touching, just as we discussed above. Again, you may have to turn on the ignition key to make them work, but this should light your brake lights. If it does, see if you can make the brake light switch work if you press the plunger with your finger- if you can, you should be able to adjust it so the pedal will operate it. If not, you will have to replace it with a new one.
If you've done all this and still haven't found the problem, it could be a bad turn signal switch (I know, you didn't realize the turn signal switch has anything to do with the brake lights, but it does.) With the two wires held together as before, key on, and someone watching the brake lights out back, with your third hand, wiggle the turn signal switch up and down and back and forth, to see if you can get even a momentary flash out of the brake lights (both sides come on at once, not just one side, which would be the turn signal working right). If you can make them work that way, your turn signal switch is going to have to be replaced. I think NAPA still stocks them. It's a tough job but I'm sure you can do it - but you need a special puller to get the steering wheel off.
I'll quit typing now - let me know how this works out for you, please.
Dick
