Brake Lights.

this 72 dart had a bad directional signal switch so i replaced it with a another used one, i got all signals working but no brake lights. since that i have checked and/or replaced the fuse,brake light lamps, stoplight switch, hazard flasher, ground wires in the trunk. i found some corrosion/oxidation inside of the taillight wiring harness plug but thats about it , im not sure where else to look?