99 F250 7.3l, the battery light came on the other day. I searched and read the posts on this subject but still no luck. Here's whats been done so far.

Removed alternator and had checked at Napa, checked out "good".

Batteries looked like the original ones. Replaced with new.

Disconnected the batteries for an hour in an attempt to clear the computer. Checked the wiring while waiting and didn't notice anything.

No change, light stays on, sometimes it flickers off but most the time its nice and bright red. The voltage gauge is still reading the same as before the light first came on. Never changes when the lamp flickers on and off. Truck starts and runs perfect only problem is the stupid lamp. Any thoughts or suggestions on what to do next would be greatly appreciated.

 

I'd try putting on a new alternator. I had the same problem, the batteries were just replaced a few months before, and the truck ran fine. The volt meter (idiot gauge) in the truck never changed and when I tested the alternator, it did show it was putting out lower volts than it should. Replaced it and it solved the problem. Just a thought, I wouldn't always truck auto parts stores.

 

Not all counterpersons are competent. But, they do want to make the sale. They would tell him in a hurry if there was something wrong with it.

 

Over the past couple of months I've been going to the same Napa store and working with the same counter person. He's very honest and knowledgable. Maybe his test equipment is just incorrect. I'll pull the alternator out again and get it checked someplace else. I need the truck this weekend for a long trip and would like to get this fixed.

 

If it's not your alternator, it might be some wiring on your truck. If you can, test it yourself, or take it to your parts store and have them do it. Just take a volt meter and put it to your battery, you should get somewhere between 13-14 volts when the truck is running. When I tested mine, it was right around 12v, which meant the alternator wasn't charging, I was just running off the batteries.
Hope you get it fixed soon.

 

Solved the problem this morning. I took the alternator back off and had it retested by a couple different places. Sure enough its dead.

I did get a break on the cost of a new alternator at the Napa store though. Everyone makes a mistake now and then. Installed the new one works good and the light went off. Thanks for the input everyone.