Chart B To B-5: Pump/Motor & Brake Light CKT

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1988 Cadillac Fleetwood, 1988 Cadillac DeVille, 1987 Cadillac Fleetwood, 1987 Cadillac DeVille, and 1986 Cadillac Fleetwood. However, it is still accessible from the selected car via links, so may be relevant.

Pump/motor assembly is designed to provide hydraulic accumulator with specified pressure. Pump/motor is controlled by pressure switch. Pressure switch closes, which activates pump/motor. This circuit grounds relay coil.
Positive circuit for relay coil comes from 5-amp pump relay fuse. Power for relay comes from 30-amp fuse, located in engine compartment. When pressure drops to 2030 psi (14,000 kPa), pressure switch circuit closes, grounding relay coil.
This activates relay allowing pump/motor to operate. When pressure reaches 2610 psi (18,000 kPa), pressure switch circuit opens, deactivating pump/motor. "BRAKE" light circuit is powered by 20-amp gauge fuse. Circuit is grounded if parking brake is applied, fluid level is low or pressure is low.
Pressure switch will open when pressure is below 1500 psi (10,350 kPa). Switch will close when pressure reaches 1900 psi (13,100 kPa). When fluid level is low, fluid level switch float opens circuit, turning warning light on.

Fig 1: Chart B Hydraulic Unit Functional Check (1 of 2)

Fig 2: Chart B Hydraulic Unit Functional Check (2 of 2)

Fig 3: Chart B-1 Pump Does Not Run

Fig 4: Chart B-2 Pump Runs Longer Than 45 Seconds

Fig 5: Chart B-3 Pressure Switch Performance

Fig 6: Chart B-4 "Brake" Light Circuit

Fig 7: Chart B-5 Hydraulic Unit Leakdown