1994 300Tdi glow light blinks on quickly


New member
Hi lads,

First post here. As the title says, I’ve got a weird issue when I turn the key to heat the glow plugs, the light literally blinks on and off very quickly, stays lit for less than a second. Mind, when I got the truck (somewhat recently) the light didn’t come on at all and so suspecting a bad relay, replaced it, so now although the light does illuminate, it doesn’t seem to stay on long enough. Here in Ohio, it’s in the 80s F during the day and as of late, been in the 50s at night but the light behavior remains the same regardless of ambient temperature. I understand it should light for maybe one second on a hot engine and maybe 2-3 seconds on a dead cold one, which makes sense to me based on prior experience with Mercedes diesels.

If anyone has any suggestions, I’m open to hear. The truck starts fine but want to make sure the system is fully operable before winter. Possible the new relay internal timer could be faulty I suppose but I wasn’t sure if this system has any sort of self-diagnostics like the Mercedes systems do.



Well-known member
it's a straightforward circuit. grab a meter and locate the fault. guessing the relay shuts off and is faulty.