This is a 1999 Cherokee with a problem. It will often lose power, gauges go wild, head lights go dim. Mechanic replaced alternator and we've cleaned all grounds with no change. One mechanic tried on hooking air bag for some reason, still no change. Jeep automatic transmission often is in high gear when starting from a stop which might be the reason for power loss a other times while moving.

Any ideas?

 

Pull the cover panel and check behind the fuse panel. Check for corrosion.

 

I had the same problem (99 xj sport). Battery had a dead cell, but still reads 12V when measured. Replaced battery, and all was good.