1970 C10. Recently rewired entire truck. Electrical was working fine after rewire. Stopswitch went bad (was not replaced during rewire). Replaced stopswitch (two prong variety), but only right rear stoplight works. Both turn signals work. Still uses stock 1157 bulbs. Bulbs are fine. Trying to figure out where the issue is stemming from and what to do to remedy the issue.
The wiring for lights on a 1970 C10 is pretty simple,
Going by what information you’re giving, I would have to say the turn signal switch has a bad contact inside it.
The brake lights go through the turn signal switch.