Noticed here lately sometimes I turn the key on to start the truck and there's no buzzing from the fuel pump- gauge stays on zero. If I turn the motor over it spins but no run. If I turn the key off and back on the pump buzzes and the truck starts right up. Is this possably the ignition switch? A relay somewhere? Something more serious? I have the aftermarket pump setup (the good one) mounted to the frame and the one on the engine bypassed. This is a 98.5 24 valve Cummins. Any ideas? Thanks-

Testing with a multimeter or test light will answer your questions.

I STRONGLY urge you to read this article ASAP. That injector pump is dependent on the proper supply of diesel fuel to lube and cool that pump. A failing lift pump will kill the injector pump.

It sounds like you've got a lack of power to the injection pump when the lift pump isn't working. The injection pump should have enough suction to bring fuel through the lift pump if it's not working. As stated, I'd get a test light and start doing some investigating to see what you can determine. Any info might help narrow it down.