K 3500 Truck 4WD V8-454 7.4L VIN J SFI (1996)
Vacuum Gauge/Economy Meter: Testing and Inspection
The fuel economy warning light should go on when the ignition is turned on. If it does not light, disconnect the wire from the fuel economy vacuum
switch connector and ground the wire to the frame or cylinder block. If the warning light still does not go on, check for burned out indicating bulb or an
open in the harness between the vacuum switch and instrument panel. If the warning light goes on, circuit is functioning and the vacuum switch should be
checked for proper ground. Remove and clean the mounting bracket screws and the mounting surfaces.
If the warning light remains lit when it normally should be out, check vacuum hose to vacuum switch for damage or plugged condition.
If system still does not operate correctly, perform the following steps:
1. Disconnect electrical connector and vacuum tube from switch.
2. Connect a self-powered test light to the switch electrical connector and to the vacuum gauge mounting bracket.
3. With vacuum applied, test light should be off.
4. With no vacuum to the vacuum switch, test light should be on.
5. Replace switch if test light did not function as specified.
