[ChevyTech]

For C/K trucks 1988 to 1993

Brake Switch mounting – Installing:
The body of the brake switch should not move with the pedal at all.
When you have the switch removed look at the side of the switch that would be towards the parking brake pedal if the switch were still installed. There is a protrusion on the switch that must slide into an opening where the switch mounts. Somewhat like a big square lug into a slot. If not installed with the Lug inside the grove it belongs in the switch will move and not stay in adjustment.

Brake Switch adjustment
Here is how the switch is adjusted:
On the curved side of the switch, which is pointing down and somewhat towards the front of the vehicle when installed, the end of a lever protrudes slightly out of a slot.
While holding the brake pedal down a little ways, slide the lever that protrudes from the slot toward the driver’s seat.
Let go of the lever, then return the brake pedal to its fully released position, and the switch should self adjust.