need help gmc brake booster wiring

[rip van sparky]

Hi, was wondering if anyone had any experience with the gm hydroboost. My 88 c6500 emergency brake booster circuit is not working properly, the pump still works when wired direct, but the circuit is screwed somewhere. I replaced the relay, it works, but not with the brake pedal, the activating circuit is live all the time, and the ground switches are not working. There are alot of wires and diodes and things under the dash, I really need a schematic. thanks, John

 

[typ4]

I assume you are talking about the Bendix Hydromax with the motor under the actuator. I would rewire it to the way international or ford does it, GM may be the same?it is easy, they ground the motor thru the pressure switch and control the power thru the brake pedal switch and a relay. when the hydro pressure is up the ground switch opens and shuts off the motor.