'93 glow plugs and controller story

[Rare93Turbo]

Posting in case it helps someone. I recently replaced all my glow plugs as a preventative measure. When I bought the truck I discovered that when they get old they can break and fall into the combustion chamber (while replacing head gaskets I could see one piston had a bunch of dents on top that were obviously the shape of a glow plug tip). So, recently I made the mistake of getting Autolite brand. 4 of them burned out in a week or two. Discovered they are rated at 5 volts whereas the Motorcraft are rated at 10.5v. Will only buy Motorcraft from now on.
Second part of my story, When I put my old glow plugs back in nothing worked. I traced and tested and finally put in a new controller but nothing changed. Finally, on a whim I ran a small jumper from the controller black ground wire to the battery negative and everything worked normally. Moved the ground wire from the controller mounting bolt (where it has always been) and put it on a valve cover stud. System back to normal.
I read many posts where people were trying to diagnose bad glow plugs using an ohm meter. They can short internally and not heat up so the ohm meter reading will mislead you to think it's okay. I like to test by applying voltage for 3 or 4 seconds. It's pretty obvious using this method whether they are good or bad.

Over and out - Happy 2025