There are many advantages to ground switching. It's normal for the light to flicker when you hit the brakes.Our MASTERCELL uses ground switching to control all of the electrical functions in your car. This provides a path to ground to the Brake Warning light which lights telling you there has been a drop in pressure and you should check it NOW. If however the pressure drops in either circuit due to an internal leak in the master cylinder or a leak in the lines pressure will drop and the switch in that circuit will close. If the master cylinder generates enough pressure in the front and rear circuits then the hydraulic pressure switches (44) will OPEN breaking the circuit to ground and the Brake Warning light on the dash will remain OFF. Power from Fuse B goes through the brake switch green wires to the turn signal switch and on to the brake lights which will light. If you press the brake in this condition BOTH switches in the brake switch close. Now with the Emergency Brake OFF and key ON. It's normal for the light to flicker when you hit the brakes. Since the hydraulic pressure switches are already closed there is a complete path from ground through the emergency brake switch through the dash light to the fuse and the Brake Warning light lights telling you the Emergency Brake is on. If you pull the emergency brake handle, switch 40 will close. Because the key is not on no power is applied to the dash switch so it will not light even if there is a problem. This sends power from Fuse B through the brake switch (42) to the turn signal switch (43) and on to the brake lights which will light. If you press the brakes in this condition you close BOTH switches in the brake switch. So with the key off and brakes NOT applied the dash (41) light and the brake lights are off. The hydraulic brake pressure switches (44) are closed when the brakes are NOT applied which grounds the red wire on one side of the switch (42). (The brake lights go through the turn signal switch.)Ĥ4 are the hydraulic pressure switches on the dual master cylinder. The pic is confusing as hell but it is accurate.Ĥ1 is the brake warning light on the dashĤ3 is the turn signal switch. The attached pic shows how this is wired. The red wires are part of the brake check circuit on the dual master.

If you don't have a dual master with the brake warning switches then you only need the two green wires.

If you have the time you can take the switch apart and clean the contacts and check the springs are not broken or out of place.

Brake light switch diagram