For a simple check of the operation of the vacuum circuit breaker, proceed as follows:
1. Block the wheels with suitable wheel chocks.
2. Release the parking brake and check the brake fluid level.
3. With the engine off, press the brake pedal more than 20 times.
4. Start the engine and check if the brake lights turn on when you press the brake pedal.
5. If the brake lights do not turn on, turn off the engine and depress the brake pedal again more than 20 times.
6. Disconnect the connectors from the vacuum switch and check the continuity of the circuit between its outputs.
7. If the circuit is open, replace the vacuum switch.