1969 roadrunner brake lights

I have only one stop light coming on, and I've checked everything I know to do and I can't get the other to light up, everything else is working fine the running lights the blinkers Everything has a good ground I change the brake switch, I replaced the rear harness,
I replaced the flasher switch, all the bulbs of course and still can't get the left side to light up. Has anybody had a similar problem? I can use the help!!! Thank you

Do you have a test light?
Connect it to a good ground.
Touch the tip to the socket while someone presses on the pedal.

BTW, isn't the turn signal the same circuit and bulb filiment? If it is and you do not have power with brakes, it's going to be the TS switch.

The only thing is that I am getting power to one side of the brakes and not the other...

Rod is right, the turn signal and brake light would be the same power feed either brown or dark green depanding on which side your talking about. does the turn signal on the failing side work? do you have a diagram?

If the turn signal lights the bulb on the affected side, but the brake application does not, it's the turn signal switch - can't be anything else.

OP didn't say which side, but...

One way to test is disconnect the turn signal switch harness at the base of the column, apply 12V power to the (IIRC) light tan wire in the dash-side harness of the turn signal switch harness connector. If the right side illuminates, everything to the back right side is working. Light green is for the left side. Same story.

Yes, thank you for your help, it was definately a bad turn signal switch.