Basically the light means your alternator is not charging. You need to find out why.
First you might try revving the engine to see if it goes out. If it does, checkthe serpentine belt for slippage. Then, check connections to the alternator and battery. Look for dislodged connectors, frayed or broken wires in the harness, etc. Wiggle things. Then, if you can lay your hands on a voltmeter, you check voltage at the battery to see if it's charging. If it isn't, you can assume you have an alternator problem. If your Jeep has high mileage, as it probably does, it could be worn brushes and dirty slip rings. Take something like a hockey stick or a broom handle, and (being careful not to get your body parts or the stick entangled with moving parts) tap the alternator while it's running. If the light goes out, it's diagnostic for bad brushes. If it doesn't, then it could be that or worse. Either way, you will need at least some maintenance if not replacement of the alternator.