The left brake light on my 67 does not work, but the right side does. I swapped bulbs between the right and left to make sure it wasn't the bulb and same thing - left brake light doesn't work but right still does. Then my son discovered that the left brake light will work only if you have the left or right turn signal activated at the same time. Can any of you electrical gurus tell me if those circuits are connected some way in the turn signal switch? I was planning on replacing the turn signal switch anyway because the right turn position won't hold - you have to hold the lever up to activate the blinker. I guess the cam is broken. I was hoping to just get one of those cam replacement kits for $10 as opposed to the entire assembly for about $75. But if my brake light problem is linked to the turn signal switch, then I'll replace the whole assembly.

 

Its always the ground.If you are positive you have the correct bulb then you need to check for complete grounds. The tail light assembly should have a ground that mounts somewhere in the trunk area. Not far from the bezels. The fact that the light works with the turn signal on shows you that when the signals are placed into the circuit a ground is found. When the turn signal switch is out of the circuit the light has no ground. Remeber the bulb needs to have three elements, tailight,turn and brake also.

 

I had a similar problem with goofy light problems. I ended up having to replace the whole turn signal assy.and the wires in the steering column. I got the part from Mustangs Plus I believe for $27. For your car it is part no. 00182 and $79.

With mine, the plastic peice that the cam sits on was warped.

 

I would have to go with the switch assembly. Sometimes you can fiddle with turn and emergency and get to work, but it usually don't last. You will need the whole thing.

 

Thanks for the suggestions. I'll check the ground first, then work my way towards the turn signal assembly.

 

The turn signal 'overrides' the brake light function. One more vote to check the ground (easy) and then replace turn signal switch.

 

Agree. U'r gonna end up replacing the whole switch.

 

The wiring circuit for most, if not all, combination brake and turn circuits has the brake light switch feed the rear lights thru the turn signal switch assy. Your problem ismost probably the switch. Typically, if you have a grounding problem at the light, the voltage from either the tail or turn circuit is backfeed thru the light bulb filaments creating a dim issue or erratic operation with the running lights on versus off..

If you want to really make sure, using a test light (2-10 bucks at auto parts stores) pull the bulb and ask an asistant to step on the brake with the TS switch off and you should get a light, if not, do the same with the lever in the left or right position, it should still come on if it is the correct direction (left bulb- left turn selected and vice versa). If you don't get a light when off but do when on its the switch, if you don't get a light at all, it could be the switch or the wiring.