67 Dart Brake Lights

The only ground required is at the bulb sockets so if they come on ground is not the issue. Brake pedal should return to push the switch button. That opens its contacts, lamps go off.
The only return spring is inside the master cylinder. That should be a constant, yet we've seen cases where the pedal arm doesn't align with the switch button. Switch bracket bent? The pedals pivot points worn? Firewall distorted at the master cylinder? Who knows?
Hopefully you can push the button with a finger and the lamps will go off. From there its a matter of adjustment. A single small screw ( 1/4" hex head? ) attaches the switch bracket. Loosen that to adjust switch position up/down. You would have to bend something for left/right adjustment.
Good luck finding that mouse too.