'99 7.3 PSD/SD

Last 2 or 3 weeks, the battery light on the instrument panel has been coming on occasionally. It might stay on for 2 seconds - at other times maybe two minutes (or longer). Can't seem to find a pattern here.

A week ago the light stayed on all the way home from work (about 45 minutes).

I have not driven the truck for about a week.

Yesterday, I had to charge both “new” batteries sine each was down to about 5 volts. Not surprising if they're not charging since I have an inverter that runs 24/7 (I've pulled the fuse).
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1. Cranked it up 30 minutes ago, checked voltage on both and found 12 volts only.
2. Checked Alternator output and initially no voltage.
3. Re-checked batteries and found 14.2 volts.
4. Re-checked alternator - found 14.2 volts
5. Opened the door to check if bat light was on – no light.
6. Rechecked the bats – “0” (zero volts)!
7. Rechecked the alternator – no voltage.
8. Checked the bat light – it was now ON!
9. Rechecked the bats – 14.2 volts
10. Rechecked the bat light – now OFF!
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What the heck is going on? Alternator? Computer? Something else?
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Thanks in advance to the forum.
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Clif

 

I don't know what the above means, but there is no way you are going to get zero volts at the battery, and the truck is still running.

I would check for loose connections at the alternator. Fiddle around with them, unplug them and inspect them for melting. If that doesn't fix it, I would suspect worn out brushes in the alternator.

 

When I got to work I left the engine running and checked the voltage at the battery terminals - "0". I checked the output of the alternator with the engine running: again - "0". The Battery Light was still on and the voltage gauge (whatever it's good for) was reading around 13 volts.

I shut off the engine, checked the voltage at the battery terminals - 12.20 volts.

I hear what you say - but it is what it is. Got me confused for sure.

 

sounds like a bad plug on the alternator. my 02 did the same thing for 2 years before i finally changed the plug after i got stranded 100 miles from home with dead batteries

 

my truck is doing dam near the same thing but i have dual alt's
Ive changed one of the plugs i guess i will pick up another on the way home tmmr

although im getting a draw of .18 on my multimeter when checking for a draw from my gem its driving me crazy i cant imagine that plug would cause a draw and it only acts up in the winter

 

My apologies to all who responded as I thought I had told everyone what the end result was. Getting old, i guess.

Turns out there was a gradual cascade failure of the diode trio in the alternator. Intermittent operation at first then the whole thing went down. My comments about zero volts at the battery were due to bad VOM leads. Sorry.

Replaced the alternator for $106 at a local Advance Auto Parts with a lifetime warranty. All better now.

Again - apologies for the delay in responding. Thanks to all for your comments and assistance.