Brake pressure switch?

Question

Wondering how a brake pressure switch works? What makes the break light turn on?

more or less im looking for how the tail lights come on when the brake is pressed.

Answer 1

The brake proportioning valve has a piston in a bore that is in between the front and rear brake system's lines...there is a plunger type switch that screws into the prop valve and rests on that piston when it is normally centered in the bore. If either front or rear brake system loses pressure, the piston will move off of center, allowing the plunger of the switch to come out and make contact internally, thus turning on the warning light. Look in a service manual for a cut-away view of one to beter understand it.

Answer 2

Brake pressure switch? There is no such thing. Are you talking about the brake warning light in the dash and what would cause it to come on?
A loss of brake function at the front or rear end of the vehicle could make the light come on. The light in the dash is hooked to a switch inside the proportioning valve (located under the hood). If you were losing brake fluid, say from a broken brake line, the proportioning valve would sense the loss of brake pressure on either end of the vehicle and the light would come on.