From the Truck Forum posted by AirSpeed
I have driven off with my parking brake partly engaged on a couple occasions and today I had a brain flash! I mounted a brake light switch that is normally open on the parking brake bracket, I grounded one of the two lugs to the bracket and ran a wire from the other lug to the brake wire on the master cylinder. Now when the key is on and the parking brake is engaged the “brake” light in the dash lights up until I release the parking brake. It was a ten minute operation and works perfectly.
One side of the switch goes to the ground lug, the other to the wire on the Master Cylinder.
Updates to the thread were made by Bruce88 and include this.
Since my parking brake assembly is not installed it was easier to show this mod with some dimensions and a wiring diagram. If you’re interested see my build (post #421) http://67-72chevytrucks.com/vboard/s…60#post4264460