Warning Light Does Not Come On During Bulb Check

If warning light does not come on when ignition is turned on with engine off and parking brake disengaged, check for burned out bulb. If bulb is okay, check for open in circuit by unplugging connector from differential pressure switch on brake combination valve, and grounding wire at connector with jumper. If warning light does not come on, repair open in circuit. If light comes on, circuit is okay. Replace differential pressure switch.