I have a '99 F-150. My battery light use to come on only when I would be on the interstate recently and or whenever I would get over 65-70 mph. I just was driving on it the other day and would watch my battery gauge and it would slowly go down. I would get off on an exit and whenever I would drop below 65 mph the light would go off and the battery meter in the truck would shoot back up to normal.

The other day it started to stay on for good. I went and got my battery and alternator tested and both were good. Today I looked at all the wires, disconnected them, made sure everything was fine and then drove to class and back. Now my truck won't start and the battery is dead. What could it be if the battery and alternator are good and all the wires look fine? Could the alternator maybe just be bad anyways if the autozone battery checker thing said it was good?

I've been told to load test it. How can I do that?

 

charge the battery then go buy a new alternator.

 

Yup. You need a new alternator.

 

Thanks. I figured that's what it was. I have to charge the battery on a charger first right? If I try to charge it with my alternator, that is just gonna burn it up probably? Looks like it's time to take out a loan, haha.

 

You could charge it with your alternator, but how are you gonna get the engine cranked in the first place? Also, If it's been a few hours since your battery went dead, it probably has already charged itself back up(if it's a good battery).