New alternator not charging

[jollyjerry]

I bought and installed a new alternator, but when I tested it running, I noticed it wasn't charging at all. Here's what I've gone through:

• Battery is good and charged. 12.6V when the truck off
• Alternator doesn't seem to be charging. 12.3V when truck on and idling. Lower if accessories on.
• Belt looks tight and alternator pulley is spinning
• Continuity between ground and the alternator case
• Continuity between the alternator charge stud and the positive battery terminal
• 1-wire connector pigtail snug. Couldn't see where that wire lead to, don't know how to test this wire
• Wire from positive battery terminal to fuse relay center looks good

I wish I tested the old alternator before I returned it for a core fee to see if it was just charging poorly or not charging at all. What else can I try before I assume the new alternator is bad?

 

[chipskittles]

The one wire on the pigtail goes to your dash light. What's your battery light on the dash doing? It should light up with the ignition on but engine not started. If it doesn't then the bulb may be burned out or you have a wiring fault. Field on the alternator will not energize if there is a problem with the bulb or related wiring. I thought they used a resistor in the circuit so the light bulb is not necessary on the GMT400 but I would not assume. Battery light should stay lit with the engine running if the alternator is not working at all.

 

[jollyjerry]

Yep, bonus idiot points for me today. Gauges were unplugged, so it wasn't charging. Worked great after. Old alternator was probably fine, but at least the one I got was cheap-ish at $60.

Thanks for the help!

 

[davkenrem]

Resurecting old post to add a thanks. My alternator stopped charging the other day. Got a ewn alternater, Lifetime warranty replacement. This one didn't work either, knew the problem was not the alternator. Started searching here, this was the second post I looked at. and you mentioned instrument cluster!!! DING, DING, DING!!! I had the instrument cluster out last week while I was drilling some holes in the dash (long story) any way I knew this had to be the culprit. My battery was light was not coming on. I go pull the cluster and there is some small pieces of plastic in the cluster connector, blocking the only the alternator circuit. Cleaned it out and "VIola" charging again. Fantastic!! Thank you all for you posts!!!