Nope check the bulb in ur instrument panel first. Tiny bulbs do burn out. On time for glow plugs is actually commanded by the pcm and not the idm if a 7.3L. depending on the year u have a glow plug relay that looks like a starter relay or a gpcm. To Test the starter style relay there are 2 large wires one will have constant 12v the other will not until u turn koeo ( key on engine off) once that's been done the other large wire ajasent to other will receive 12 v as well and the pcm will shut it off depending on vehicle block temp. If it doesn't “ jump" to other terminal ur relay is bad and needs replacement.