I have a 1997 F150 4x4 w/4.6L eng. Battery Charge indicator on dash stays ON. Battery was 5 years old and alternator was original. Installed a new battery...no help. Then bought and installed a remanned alternator, then topped off the NEW battery with a charger, then connected up the neg terminal on the battery, and started her up. Started up fine, but the battery charge LT is still ON!

NOW I troubleshoot (yea, should've done some T/S first, but was lazy).

Battery reads 12.8 V across terminals with neg terminal disconnected, and 12.7 V with neg terminal connected (engine off). Then started the engine and revved to 1500 RPM and battery reads 12.4 V (not good, right?). Turned everything off and disconnected the neg battery terminal and measured the output post on the alternator @ 12.7 V (good , right?). I also measured continuity between the negative battery lead and alternator housing.

I think I checked all the fuses and even swapped a couple relays around, but without documentation, I am not certain I checked all I could. The owners manual is weak. There's a relay box next to the fuse box under the hood that is not even mentioned in the manual.

Any other clues? Where can I find a good schematic?
Maybe I bought a defective, remanned alternator?

 

Look in that box for an Alt fuse. It could be blown. It's not charging right now.

 

make sure you got a good ground on the terminals of alternator. make sure the plug on the alternator is pushed all the way in. dont pull any wires off the alternator or battery with it running, not good... the alternator needs the battery as a reference point to work. the alternator should be putting out 13.8 to 14.5 volts when running and connected to the battery. if everying is tight and grounded good, i would take the alternator back and have it tested just to make sure it is o.k. could be a wire or plug on the small wires to the alternator is bad, but i would bet more on the alternator.

 

Well, here's the rest of the story. The first alternator I purchased turned out to be defective. Actually it was a core that someone else turned in and somehow ended up in a box on the shelf.
I took the new/old alternator to a different parts store to have it tested and it tested good. (The first store's bench tester was 'down').
I then removed the harness to/from the alternator & used emory cloth to clean every contact, connector, mega-fuse contacts, etc. Measured resistance from pin to pin....all good.
I then went back to the second parts store and had them test my original alternator and it popped the circuit breaker on the their tester. Definitely bad. Since the bench tester showed the new/old alternator was putting out enough voltage to 'pass', I thought maybe something else was faulty on the new/old alternator such as the regulator (P/O alternator). So much for testers. So I bought another new alternator.
I put the second new alternator in the truck. topped off the battery, and the truck is back up and running.
By the way, the second store called the first store and told them they sold me a 'core'. It was easy for them to tell, even though it passed their bench tester. When I went back to the first store they did refund my money and apologized for the mistake.
Confused? So was I. And my truck was down for two weeks. End of story.