My 1952 3100 truck was long ago converted to 12v, and all the lights worked well (incandescents). But to get authentic looking reproductions and bright light I chose LED taillights from LMC motors. The old taillights were just trailer lights with three leads: running, brake, and turn signal, powering one single filament bulb and one double. They were activated by a toggle under the dash. Ugly but worked!
The LED taillights are three leads: running light, brake & turn, and ground. I changed them out (including the LED compatible flasher) and connected the wires according to the diagram (brake and turn sharing a lead), but now I have running lights and brake lights, but the turn signals both blink at once. Taillight manufacturer told me the toggle wouldn't work and I replaced it with the steering column clamp-on unit from LMC with the same results.
Incidentally the new turn signal switch has an emergency flasher which works fine, as do the front turn signals (incandescent).
Any advice for the amateur electrician?