Originally Posted by somewhereinusa
You don't want glow plugs on anything to be on when the engine is running, it will cause preignition. Like pinging in a gas engine.
As I understand it, glow plugs on the 7.3L do stay on for 30 seconds or so after the engine has started. When watching my digital battery monitor I see my starting bank voltage staying down around 11 volts until I get out the driveway, then it pops up to 14.x volts.
As everyone here said, no problem driving with dead glows. It may be harder to start but once you're running it's all good.
If your bus has OBDII diagnostics many auto parts stores will scan your error codes for free.