3500 4x4 Pickup L6-359 5.9L DSL Turbo (1996)
6. Apply 8.5 to 9 inches of vacuum to warning switch and observe warning lamp. If lamp goes out, switch vacuum hose is either loose or leaking. If
lamp remains on, leave engine running and continue testing.
7. Apply 20-25 inches vacuum to switch and observe warning lamp operation. If lamp now goes out, switch is at fault and should be replaced. If lamp
remains on, continue testing.
8. Connect vacuum hoses and replace original warning switch with known good switch. Run engine and observe warning lamp operation. If lamp is
now off, old switch is faulty. If lamp remains on, problem is in wiring between switch and warning lamp.