My work truck, 96 Sierra 3500 Pickup clicks but won't even turn over. It has been sitting for a few weeks. Battery is brand new and lights are bright. I'm guessing it's the starter. Any way to diagnose the starter to be sure? I guess the solenoid in the starter clicks but the truck still won't turn over. Would tapping on the starter help it to start? It never showed any problems with starting before.