diffra

So, to explain the situation, My truck (88 22re 4x4 w/bed from an 89+) been with my dad for the last few years while I've been overseas. I'm coming back soon (next week) and then moving back for good in a few months, and will be using the truck as a daily driver. He's been told by his mechanic that the alternator is overcharging and that's why he's gone through 3 batteries in the last few months, while barely driving it. It seems like it should just be a matter of replacing the voltage regulator (and probably the brushes while I'm in there) The question I have is, is that even possible on these? It's something I've read quite a bit about but never done myself. Where would I source the VR (I can find the brushes fairly easily)? Would it just be easier to replace the alternator as a whole? Lastly, do I need to do anything special to tension the belt properly? Any info would be super helpful. Thanks!