Caller Bill with the 1972 Porche. It smokes any time he turns off lights while engine is on.
Bill should pull over next time this happens and see if the headlights remain dimly lit even when they are turned off. It’s possible the headlight circuit is shorted to a small guage wire somewhere in the wiring harness that is at 12 volts when the engine is running. This wouldn’t cause a problem when the headlights were turned on, as it would just short out 12 volts to 12 volts. No current would flow. When Bill turns the headlights out, all the current to the headlights is instead routed through a wire not designed for that much current. The over-current condition would smoke the wires, and the voltage drop in the wiring would cause the headlights to only light up dimly.