* Glow Plug Relay: This is the most common culprit. The relay switches power to the glow plugs. It could be failing, stuck open (always on), or stuck closed (always off). Testing the relay with a multimeter is crucial.
* Glow Plug Control Module (PCM or ECM): The engine control module (sometimes called a PCM or ECM) governs the glow plug system. A faulty module won't send the signal to activate the relay. Diagnosing this usually requires a scan tool.
* Glow Plug Indicator Light Bulb/Wiring: It's possible the bulb in the instrument cluster is burnt out, or there's a break in the wiring to the indicator light. Check the bulb and wiring for continuity.
* Glow Plug Wiring: Check the wiring harness connecting the glow plugs to the relay. Look for broken wires, corrosion, or loose connections.
* Glow Plugs Themselves (Less Likely): While possible, it's less likely that *all* glow plugs failed simultaneously. If the indicator light doesn't work at all, faulty plugs are lower on the list of probable causes. Testing each glow plug individually with a multimeter is needed to confirm their operation.
How to Troubleshoot:
1. Check the Glow Plug Relay: This is the easiest and often most successful first step. Locate the relay (consult your owner's manual or a wiring diagram), remove it, and visually inspect it for damage. Use a multimeter to test its continuity according to the relay's specifications.
2. Check the Glow Plug Indicator Light Bulb and Wiring: Inspect the bulb in the instrument cluster. Check the wiring from the light to the control module.
3. Check the Wiring Harness: Inspect the wiring harness from the relay to the glow plugs. Look for any signs of damage.
4. Test the Glow Plugs (if other steps fail): Use a multimeter to test each glow plug individually for continuity and resistance. (Consult a repair manual for specific resistance values for your 6.2L.)
Important Considerations:
* Safety: Work on the electrical system with the engine off and the battery disconnected.
* Repair Manual: A repair manual specific to your 1984 Chevy 6.2L is highly recommended. It will provide detailed wiring diagrams and troubleshooting procedures.
* Professional Help: If you're not comfortable working with automotive electrical systems, it's best to take your truck to a qualified mechanic specializing in diesel engines. Misdiagnosis can lead to further damage.
The sudden failure of the glow plug indicator light often points to an electrical problem rather than a failure of the glow plugs themselves. Systematic testing of the relay and wiring is the most efficient way to diagnose the issue.
