This bears repeating:

The light for the glow plugs is only a relative indicator for "attempting to start".

The glow plugs continue to glow for up to one minute in the glow position.

Try placing the key in the glow position, wait 30 seconds, then try starting the car. If that helps, your glow plug (or more than one) may be nearing their replacement stage.

If you can "glow" the plugs for one minute and it doesn't help start the car, you have issues.

As the glow plugs age, you'll need to glow them longer for the same start performance.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)