Okay, I have a 1979 K5 Blazer. And each time I go to start it, it needs to be jumped. And midiately, I have low volts. I have put 3 alternators, 2 starters, and 3 bateries within the last year. I took the negative cable off while it was running, truck stayed on. So the means the alternator is good right? And if I drive at night I lose all electornics. Except the "Fasten Seatbelt" light is the only thing on. And yesterday I was putting a cheap voltage reader on to my battery. When it's idling the volts are okay, still low, but as soon as I hit the gas, it sucks the life out of my battery. So can this be a "Voltage Regulator" or just a "Major Short"? Anything will help.

 

It could be a bad ground, or several, they are all over the place. With a rusted / corroded ground connection, at higher current draws the voltage will drop. Driving at night headlights pull some power, may prevent relays from turning on.

You might try using one lead of a jumper cable to connect the frame of the alternator to Battery ground. This assumes the positive wire is ok, since you replaced it so many times. That bypasses engine and battery grounding to the frame.

 

I have personally not changed, the negative or positive cables. Put someone did. Most Older Blazers have the sideposr batteries. My post are on top. So someone changed it. Can that be the issue? I should just rewire all negative and positive cables?