Dear mcamara:

1) For a parallel pencil-type glow plug relay system, the GLOW PLUG light (on the dash) will keep BLINKING if any of the glow plugs is bad. If you GP light does not blink even though you do have some bad glow plugs, then your GP relay is bad.

2) You CANNOT feel them getting warm without removing them. You have to remove them and check to see whether they will become RED HOT when your GP relay becomes activated.

The reason why it's almost impossible to feel them getting warm is because an engine head is huge and heat from the red hot glow plugs will quickly dissipate into the head.

Eric