I had an electrical problem similar to this. I would be driving down the road, and my voltage gauge would go off the chart high (like 20 volts) and then the whole car would lose ALL power. no lights, nothing. then once it cooled off, it was fine. And it seemed to trigger sometimes when i would turn the heat fan speed either on or off. I am pretty sure it was the alternator about to crap out. I sold the car that way and never really fixed it lol. Also on my s10, not exactly the same, the stater was starting to go and would cause either a no crank, no click, or no power situation sometimes, and it would also kill the battery like the alternator wasnt working. So i ended up replaced everything thinking it was the alt or cables or battery and i finally changed out the starter and it ran like a champ