D100 1/2 Ton Pickup 2WD V8-318 5.2L VIN Y FI (1988)
Brake Warning Indicator: Testing and Inspection
1. Raise and support vehicle, then open a wheel cylinder bleeder valve.
2. Press down on brake pedal and observe brake warning lamp. If lamp fails to illuminate, inspect for the following:
a. Faulty bulb.
b. Disconnected electrical socket.
c. A broken or disconnected wire at the switch, located in the brake line "T" fitting, mounted on frame rail in engine compartment below master
3. On diesel models, brake lamp is also connected to a sensor which monitors vacuum in brake booster system.