Hi, I have a 2000 f450 crew/4wd , 7.3. I replaced the alternator yesterday with a 160 amp unit because it was starting to go bad, the battery warning light was starting to come on and off and while I was driving it last week with the A/C on the A/C suddenly went warm and the ammeter went down to about 9 amps. After shutting it off I charged the battery's started it and everything was OK, I decided to get the new 160 unit, I installed it and the ammeter shows about 14 or 15 amps charging, But the battery warning light stays on, I did notice the positive battery cable clamp at the point where the passenger side battery is has some damage due to normal wear and handling. Does anyone have any ideas why the warning light is staying on? the engine has no problem starting and cranks nice and fast. ANY HELP IS GREATLY APPRECIATED, THANKS, BILL
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I would check all connections to the batteries. Both ends of the cables. Also check to make sure the alt is plugged in completely and no frayed or worn wiring.
If all that checks out, pull the batteries and have them load tested. If one is good and one bad, you will still get it started but you will also still have a charging prob cause of the bad one. That can trigger the light.

Usually best to replace the batteries in pairs so you know that they are both about the same life.