I noticed the battery light on my 2000 F-150 4.6L was on this morning, went to work with no issues, started at lunch and came home, still no problem. Went to start after lunch and just got the solenoid click and it wouldn't catch and start. The engine also seemed to be idling faster than normal - it usually idles around 600-700 when warm, but it was sitting at 1000-1200 when I left in the morning (after plenty warm) and at lunch. Also, the needles on the gauges jump / peg all the way over when turning on the ignition.

I know first check would be voltage at alternator and battery - any other ideas?

 

The gauge sweep is an indicator that the cluster has lost usable power, and is recalibrating.

Start with a new battery charged on a trickle charger ( not the alternator ).

Also check the Alternator field fuse in the BJB ( aka Battery Junction Box / Engine compartment fuse panel ) Fuse #11, 20A. This is what the field is powered by and the regulator would be dead without it.

With any luck you have not toasted the alternator by trying to charge an overly low battery. Might want to check that as well, should be in the 14.4 range with nothing on ( engine running ).