glow plug issue

[BasinD24]

Hi all, hoping for a little input since I'm new to diesels. I haven't looked hard at the system yet but I want to get a lead on where to look from y'all. For awhile my glowplug system has been erratic. The dash light would come on sometimes but not others. For the last few weeks the dash light has not come on at all. It's been fairly warm here so starting has not been a big issue, infact, I can't really tell if the plugs are working or not. Is this a temperature sensitive system? Would the ambient temperature (80* or so)be enough for the system to not operate? Or is this merely a timed system that would always come on when the key was first turned to the 'on' position? Also, is the dash light indicative of the systems operation? IOW, could the system be working and just not have a dash light?

TIA
Joel S.