I have a '67 coupe. All my lights were working fine but, the other day my wife was following me & she said when I turn either turn signal on the brake lights don't work. Turn signals off & brake lights work fine. Tried the flashers & they all work but very fast. Sure could use some help.

 

Almost reads normal.
Turns & Brakes have their own power source from fuse panel.
Turns overrule brakes.
Brake lights on, then select turn, light should blink for selected direction via turn signal switch and other side should be brake light.
When checking lights, you might lift up on t/signal handle and view results.
If normal work, could be the pivot bushing is worn out and switch needs replacing.

A fast blinker is too much load for a P/N 512 flasher - bad bulb and/or corroded socket and/or bezel - disassemble, wire brush all, and reassemble.
Also, a heavy duty flasher would work better P/N 552.

 

OK, stepped on brake & lifted or lowered turn signal lever, but not so far that it stayed on. When I did this all worked fine. As soon as I put the lever so it would stay in the on position the brake lights would go out. Appears something is wrong in the steering column?

 

Let me get the symptom straight:
Headlights and running lights work fine?
Brake lights work when selected by themselves?
No brake lights on, but selected turn signal works good?
Brake lights on, then select turn, turn works, but other brake light goes out?

Turn signal switch faulty.
Yes, brake light power goes through turn signal switch from STOP fuse.
When turn selected, the selected side gets its own turn signal power from DIR SIG fuse panel/flasher.
Brake power is still going to other side.

 

Yes, what you posted there is exactly what's happening. In the mean time I pulled the steering wheel off & watched how things are working. When dir. signal is put on in either direction the brake lights would not come on. If I wiggle the turn signal lever just a little the brake light will come on (with my foot on the brake). If I put a shim between the turn signal cam activator & the inside if the steering column everything works just fine. It seems like the cam activator is going a little too far when I turn the signal on & that somehow is keeping the brake light from working. Hope you can understand my explanation. Thanks

 

If adding the shim makes things work like it is supposed to, either find a way to make the shim work, or maybe get another turn signal switch as this one may be worn out?

 

I did get a couple shims in to stop the cam activator from moving too far (in both directions). Not the right way to do it but for now it works just fine. I'll get a new cam activator & install it when I have time. Hopefully not too difficult to install.
Thanks for the help.