Voltage problems, new batt and alt
Here's the whole story, and not sure which parts matter and which don't:
2000 Cherokee (XJ) getting new fender flares, required some welding on the body. Pretty sure the guy that did the welding didn't disconnect the battery first.
Wouldn't start, so replaced some fuses. Turns out fuel pump fuse was bad. Started fine.
1/2 block later, lights went dim, lost power. Got a jump, then did the same things. OK, so I'm thinking alternator.
Replaced the alternator and decided a 4 yr old battery wasn't good either, so replaced that as well, same day.
Now the Jeep starts, voltmeter goes to 12 (should be at 14), sits for a while, then check engine light comes on. A few seconds later, voltmeter bottoms out suddenly, and check guages light comes on. If I stop then restart the car, same thing happens. Up to 12 for a bit, then check engine, sudden drop in volts and a check guages light.
Other people with similar problems usually end up blaming the alternator, but this one's brand new. I've double checked all connections, making sure they're clean and solid. I've heard one person say maybe a loose belt? Or maybe the stock ground lead off the battery is just too old and may be frayed on the inside?
Any help would be appreciated. Gotta get to Moab for Easter Jeep Safari this weekend! Thanks!