Hey everyone hoping for some help, my 04 f150 battery light came on pulling out my yard going to work and then went off, all the way to work it would flash on a sec or so and cut off. After about 20 mile the gauge dropped to about half, dead center, usually stays a tad above. When I got to work checked at the battery and it showed no charge so I pulled the alt. off and took it to a guy to rebuild but he just called me and said it test fine. My battery is new and terminals clean do not get y light came on and off and alt tested fine but showed me not to be charging. Truck still at work and haven't been able to look at it much but want advice to see what to look for tomorrow when I go to work and check it out. Thanks for any help

 

All charging systems are basically the same, however some alternators are externally regulated. This means there is a module located between the alt. and the battery. I'm not 100% sure this is the case with your truck but my 2000 F150 is made that way. Check with a parts house to see if one is listed for your truck. Even with a good battery and alternator you won't get a full charge. Also once the alt. is reinstalled, run the truck and use a multimeter and check power at the battery. Should be 13.5 to 14 volt between terminals

 

I still think it's the alternator. The regulators are picky on our 04 models. Crank your truck and take a voltmeter and check the output at the battery. Also check the connector that plugs into the alt for a bad connector or wires..

 

check both ends of the ground cable, where the engine grounds too.