[Intrigued]

:-)
Once in a while the relay wouldn't do what it was supposed to, and it would toast a couple of glow plugs, for sure. Then, the next time I would start it, the thing would only run on a couple of cylinders for a few seconds until the others warmed up. Shake, rattle, and roll!

I got pretty good at replacing them, until I figured out what was going on... I used to scarf them from engines that we swapped out: probably still have a couple stuck back in some box somewhere...