I have a 1996 GMC Sierra, 2500 4X4 Diesel. Was starting fine.
Yesterday, I turned the key on, the dash lights started to cycle, the "wait to start Light" came on for a second, then all went dark....Thought the battery was low, charged, but no difference. any ideas would be appreciated.

 

I had the same problem with mine. Mine is a 1995 silverado. I tried glow plug relay and all the ground wires new PMD and relocated it. It took me a long time to get mine to stop. It still does it from time to time but not as much about once every six months. When mine does it i use a battery charger to get mine to start. I pu tit on 40 amp setting for a few seconds and most the time that lets it start then dont have problems with it for a while. My batterys will read 12.89 volts but for some reason still need to use the charger. My new computer fixed most the issues i got it from autozone for 97 bucks. I had a few wire that plugged in to the computer that where loose where they go into the plug. For the most part dont have the issue unless my truck sits for a few days with out running it