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Home >> GMC >> 1997 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - 6.5L >> Fuel System >> Glow Plug Relay
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Glow Plug Relay

Fig 1: Typical Diesel Glow Plug Circuit
G95B35536Courtesy of GENERAL MOTORS CORP.
NOTE: To perform following test, use WIRING DIAGRAMS article.
  1. Ensure coolant temperature is less than 80°F (27°C) before beginning test. Place ignition switch in RUN position and allow glow plugs to cycle. After 2 minutes, crank engine for one second. It is NOT important that engine starts. Return ignition switch to RUN position. Glow plugs should cycle on at least once.
  2. If glow plugs do not cycle, disconnect relay (relay is located on top rear of engine). Connect test light between Pink wire terminal of harness connector (terminal "A") and ground. With ignition switch in RUN position, test light should be off. Test light should illuminate when engine is cranked.
  3. If test light does not illuminate as specified, repair short or open in engine harness Pink wire. If test light illuminates as specified but glow plugs do not cycle, replace relay.