Reread Hotrod Lincoln's reply above.
The switch has nothing to do with ground. The brake pedal holds the switch open when the brakes are not applied and the lights will be off.
When the brake pedal is depressed to apply the brakes, the switch arm moves to the closed position and takes power from the headlight switch/ammeter and sends it to the lights.
The ground for the lights is at the bulb socket in the tail light. No switching of ground, just like he said.
Mac :{)
1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things
| 
