The brake light switch is a pretty simple switch. it has power coming in (whatever color that wire might be), That power comes from the fuse panel. When the brake pedal is up, the switch is open, and no power goes through it. When you step on the pedal, the switch is turned on and the power goes through the other side. (Newer brake light switches with cruise control can have up to 6 wires from the brake switch, if you don't have 6 wires, we won't go into that). If there are 2 wires coming from the out put side, both of those wires should go to the turn signal switch.

From the brake switch, the power should go to the turn signal switch where it will be separated to a left and a right side, so the brake light can be canceled for the turn to function. If you jump past the brake light switch so the output wires are powered, you should get another power source coming into the turn signal switch, and that power should supply power to both rear turn/brake lights individually, through the turn switch. Gene

The only service manual I have available right now is a 78 Van, and the turn signal switch in it only has 8 pins. I would give you the pin out of the turn signal switch.