Yesterday on my way back from town My voltmeter dropped from 14 all the way down in a split second. I drove another 40 miles and the lights never seemed to get dim and nothing else seemed to be unusual. I stopped at an Autozone and they tested the alternator and and it came up that the output wire had low volts but the alternator itself showed good and the batteries showed good. Any help on this issue is much appreciated. It also started up perfectly this morning but the guage was still down around 9 volts.

 

Check your fuses especially in the PDC there is a big 12 volt fuse to the alternater. Do all other gage lights on dash work ok...Tach Ok? The regulator function for the alternator comes from the computer...either ECM or PCM I believe on your year.

Edit: Maybe you have a faulty Alt gage. Go to the big red lead on Alt and make sure you have 13-14 VDC there. There are 2 leads on alt that go to PCM/ECM and I'm not sure what to read there but thats how the Alt gets regulated from PCM. Is that the output wire that you said measured 9 volts and not the red lead to battery?

 

How does the alternator test "good" when the OUTPUT is showing LOW Voltage ?

I believe I would get a 2nd opinion. Better yet, pull the alternator off the truck and have it bench tested. That's the fool proof way to verify your alternator's true condition.

PITA yes, but you get peace of mind in the end.

 

Well, I had a hunch that Autozone had the machine hooked up to the wrong wire to begin with so I did take it off and have it bench tested somewhere else. Sure enough, it was only putting 7.2 V out. Got a new one, put it on and everything works great. Thanks for your responses. I thought it seemed odd as well that the output wire had low volts but yet the alternator was good. I guess that just shows sometimes your own knowledge is better than that of a hired employee at an AUTO STORE![laugh