I have a 82' Gmc K3500 diesel that won't start. It only turns over if you hear the glow plug relay click. There is two new batteries, new glow relay, new solenoid, and everything I put my volt tester on, comes up with 12 volt. Like I said if I don't hear the glow relay click, it will not start but if I do, it starts. Any idea's guy's, this is my plow truck and now I'm down and out. I thank you in advance for any ideas that could get me started again.