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You'll need a volt meter to start trouble shooting. Check for voltage at the stop light switch (orange wire is in). Then step on brake or manually trip the switch and see if 12V is at the white wire (output). Then check for 12V at the yellow and Green wire coming out of the connector on top the steering column (with pedal still depressed). Those 2 wires go to the stop lights. If you get 12V going into the column and nothing coming out, then I would guess that the Turn signal switch is bad.
Brake light circuit, check the fuse for volts on both sides. The hazards and brakes use the same fuse and same bulb and ground but take different paths so the turn signal switch might cause you some issues
I just had a '79 in the shop for no brake lights and no hazards. had power coming from brake light switch to turn signal switch but nothing coming out of column. Ended up being corroded brake/hazard fuse in fuse block from the car being kept in a damp garage. Had enough to light the test light, but would break contact when the load of both light bulbs was applied to it. Don't overlook the stupid things!