Before beginning this test procedure make sure vacuum brake booster is in good working order by following SSBC test procedure. Also check to confirm all vacuum hose connections are sealed tight and not leaking.
1) With pump running remove wire from top of vacuum switch (mounted in metal tee housing).
2) Does pump shut off?
3) If NO locate and repair short to ground in wire from switch to relay terminal #1 or short to
ground in black wire from relay terminal #5 to pump motor.
4) If YES re-connect wire to vacuum switch.
5) Remove hose from brake booster and insert pressure gauge into hose end from vacuum pump.