Before you get too carried away with anything, buy a battery terminal brush and clean the crap out of the terminals and posts. If they aren't shiny, keep at it until they are. I've seen many rigs with battery issues that had heavily corroded terminals in the contact area that prevented good charging, jumpstarting, and good starting in general.
Do that first.
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They are clean. I jump started it today and nothing. I also attached the dmm while trying to start it and there was no voltage drop. I'm going to remove the starter tonight in this blizzard and get a new one from autozone tomorrow.
1998 TJ Wrangler - 197,000 Miles - Daily Driver
4.0 Inline 6
The tensioner pulley has two points of tightness you need to address. One is the long screw that moves it up and down in the slot and you should not turn that until you loosen the bolt in the front of the pulley. Once you make the adjustment, then you tighten that bolt back up to keep the pulley from wobbling and also to lock it in place in the slot.
If you are unsure it is a good part, add one of those to the list of things you need.
Also, be cautious of your belt tension. With that style of adjuster, you can easily get the belt too tight which will take out the new pump, idler, water pump, or anything with a bearing in it that it turned by the crank pulley.
I've found a good way to test tightness without a gauge. Find the part of the belt with the longest distance in between pulleys. Then you twist the belt if it twists a quarter of the way around it is good to go if it doesn't twist a quarter of the way around loosen it. My bet is that the belt was to tight in result it strained the p/s pully to the point of failure. Not saying its what happened just its a very likely hypothesis anyways hope you get it fixed