Truck will not start

What tests have you done and what were the results? Any other observations or clues, such as head lights, interior lights, or dash lights that go out when you try to crank the engine? Does this happen at various times, all the time, or only after driving more than, say, half an hour? If the engine cranks normally at times, what do you have to do to get it to work? What are the exact symptoms when the problem occurs? Do you hear a single, rather loud clunk from the starter each time you turn the ignition switch to "crank"? A constant buzz or chatter from the starter relay? No sound at all?

Do you have a digital voltmeter and know how to use it? I can help with that if necessary. Harbor Freight Tools has a perfectly fine meter for around $8.00 or less.