I have a 97 6.5 diesel with all new heads and pump put into a 84 k20 it is all mechanical, the computer has been taken out, I recently replaced all the glow plugs, fuel filter, glow plug sensor and solenoid since . When I went to go start the truck it wouldn’t turn over and it would shut down the whole truck and the lights would dim and then after a buzzing noise came from motor, the voltage regulater was also smoking. Earlier that day it started right up but after 3 hours of sitting it would not crank.

 

Sounds like some fundamental electrical problems. Sounds like perhaps the starter shorted?