This happened to me a couple of months back. I was on some wayback road out in the boonies in the Delaware Basin in southeastern New Mexico. I had left the vehicle (a 2008 Jeep Wrangler JKU) to do some karst survey in the area and when I came back (in the middle of a thunderstorm no less) the Jeep wouldn't start. First thought, battery. Not it though, I had power to everything. Next thought starter, that would be bad. I started to think through the problem and realized that the starter and battery were not the only components in the starting system. The other two pieces of the puzzle are the starter solenoid and the starter solenoid relay. Of the two, the relay was the easiest to check, so I pulled it out and replaced it with the one right next to it, which happened to be used for the rear windshield wiper and was the same part number. I never use that anyway, so I didn't think it would be missed. Sure enough, as soon as I put that in, the Jeep fired right up. I've included an image of the relay/fuse box with the offending relay circled in red for anybody else out there that might run into the same issue. This is the easiest fix in the world, if that happens to be your problem...
