I turned the key to start the truck & there was a pop from the radio speakers & everything went dead. No lights, no radio, no engine crank. I checked my battery cables, & was looking at the fuses, when I saw the under hood light came back on. I went to start it, & the same thing happened, pop, dead. It had given no signs of a weak battery or starter, it started just fine 5 min. earlier. Any ideas?

 

Sounds like a short circuit causing your circuit breaker to open. After cooling off the circuit breaker closes again and the power comes back on. Check your starter wires for broken or bare wires rubbing.
You will need to start checking voltage drop with a voltage tester beginning at the battery. Battery to starter, starter to junction block, and so on. When you find the voltage drop the problem is in the last section of wire you tested. There could also be a voltage spike if two hot wires are touching. I would recommend getting a wiring diagram for your vehicle.