why isn't alternator charging battery as soon as I start the truck?

2000 CHEVROLET SILVERADO

167,070 MILES

MITCHF

MEMBER
5 POSTS
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I have a brand new battery and a brand new 145 amp alternator. When I start my truck the volt gauge is at 12 volts. After 10 to 15 minutes of driving it is down to 11 volts. then a few minutes later the voltage gauge will go up to 14 volts and remain there as long as I am driving. I have to go thru this routine almost everytime I start my truck.

Jul 14, 2012 at 5:42 AM

MHPAUTOS

CAR REPAIR CONTRIBUTOR
31,937 POSTS

I would be thinking a bad electrical conection have you tested the alt output directly off the alt with a multi meter or just relying on a voltmeter in the car?

Jul 14, 2012 at 6:11 AM

MITCHF

MEMBER
5 POSTS

I haven't checked the alt output directly yet, I've just been going off the voltmeter. Exactly where should I check it it at and at what setting should I have my meter on? Thanks for responding, Mitchf, much appreciated!

Jul 14, 2012 at 7:42 AM

MHPAUTOS

CAR REPAIR CONTRIBUTOR
31,937 POSTS

check at the main terminal large (bolt on) you will want a multi meter with a 20V scale or a bit higher will be ok,let me know what the voltage is there, at idle and at 1200rpm's

Jul 14, 2012 at 9:20 AM

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