My '57 2 ton has a three wire turn signal switch, old set-up had 4 lights at the rear, two were turn signals, the other two were stop/running lights. Since all the wiring and light sockets were trashed I converted to two tail lights that handle brake/turn/running. I built a circuit with two DPDT relays, each relay handles one side of the turn signal, when the signal switch is activated it closes the turn contacts and opens the brake contacts on one relay, the other relay in not affected. This allows standard trailer wiring.
