Not sure why but after I put two new batteries and a new alternator in my truck the battery light came on. I put the new batteries in since they were dead one morning when I went out to start it. I noticed the batteries were only a few months old so I thought maybe the alternator failed? Anyway decided to replace both which lead to the battery light coming on for no reason.

Took the truck to autozone to get the alt tested, checked out fine on the truck and on the bench tester. I decided to put a new belt on it anyway thinking it might be stretched out? Lights still on.

Not sure if its a coincidence but when I unplug the 2 wire pigtail connector that goes to the alt when the trucks running the light turns off. Plug it back in and the light turns back on.

Does anyone have any ideas?

 

Any idea what the actual voltage is coming off the alternator when it's running?

 

when the guy tested it it was around 14.01 then went up by a few maybe 14.20?

 

Were those lights on before the battery and alternator replacement?
Did you check the voltage at the batteries when it was installed in your vehicle and running?

 

They were not on before the batteries were just dead. I replaced both and all of a sudden the lights on. Voltage was checked with the truck running and new stuff installed.

 

If the battery light is on, you are not getting any voltage out of the alternator. Period. You couldn't see anything but battery voltage with your 14 volt reading and that seems high.

Since your batteries are new, expect to see 12.6-12.8 volts at terminals static.

Check your voltage on the large terminal on the back of the alternator. It should show between 13.6-14.4 volts, but probably at the lower end with fresh batteries.

Also, make sure the two wire plug on the back is secured, re-plugging in and out to ensure.

When running, you can carefully put a long screwdriver on the alternator pulley and feel a magnetic field if operating. Wouldn't be the first time an alternator, particularly rebuilt, failed.

A vom is your best friend right now.

 

Follows this from the service manual, indicating the problem is in the alternator ....

 

Just a wild *** guess. Did the PCM set any charging systems code(s)? With changing the batteries, it should have set the 1000 code. If so, you may need to clear the codes before the light will go out.


Ed

 

I've had the P1000 code many times changing around my electricals and never had the not battery but alternator light on.

 

The first time i replaced my alternator with an Autozone 140 amp i immediately had the alternator light on. In my case the terminals did not fit the studs on the alternator exactly like the factory terminals had. The terminals were not nested all the way down making proper connection. Check the simple things.

 

Check the negative grounds to the frame on both sides to make sure they are clean and tight.

 

well put a new alternator in the truck and took it for a ride. no battery light!!

 

. .

 

I wonder if it was just this ^^^^^^

But it is fixed, so no matter...

 

I didn't think it was just the connector. Maybe on a first install, but he had it tested on the vehicle then took it off and had it bench tested. He also mentioned the changes when the connector was off to when it was on. That's a whole lot of movements to have it consistently not clicked in. Plus we've had store rebuilds fail out of the box so my confidence was with the installer.

I finally just changed my connector to make the wires longer as with the height of the L-N they are in tension. And I've flipped alternator sooooo many times if there was a fatigue issue within the connector I should have been the poster child.