Late 1999 F-250, 7.3 of course.

I took a short trip today to pick up some furniture and when I got home my battery light came on. It only lights up at idle, and I think only when in park.

The volt gauge still shows where it always does, about 2/3 of the way through its sweep.

Alternator getting ready to go or something (cheaper) I might be over looking?

If not, what's a good source for the alternator?

 

Dont trust the factory guage it is what I consider to be a "close enough" guage. I would do a test with a DVM at the batteries to see exactly what your output of the alt actually is.
It does sound as if it is the alt giving up the ghost though.

 

I agree with Jim to check the batts with a voltmeter but you might want to check all your connections at the battery and on the alt itself just to be sure something isn't loose.

 

My money is on the alternator, this has happened to me twice. The most recent time I went so far as to buy two new batteries because all the tests said the alternator was fine. Tests were wrong. I ended up having to replace the alternator, too.

 

I thought I might get off easy when I remembered I have one amplifier out of the truck since its in transit for warranty repairs. I thought maybe the power lead had came off the insulator board or something and caused the light to come on, but no, it was wear I left it.

So, yup, it was the alternator. I was getting 14.1 volts at the battery but less than 12 w/o the battery. Took it to the local parts house and it tested at just a bit over 11 volts on their machine.

Thanks to the local Advance Auto Parts everythings fixed in less than an hour and for under $160. Not too bad, really.