f150 battery light

[skeetyskeet]

Ok, here is the deal......have looked everwhere.
Driving truck at night went to use the brights and the battery light came on, took it to advance auto and tested the alternator and the battery and they said both were ok. They also ruled out a short, so does anyone have any idea what this could be? This only happens when I use the bright lights.
Thank you

[skeetyskeet]

Doesn't anybody have a clue?

[unclebubbles]

Originally Posted by skeetyskeet

Doesn't anybody have a clue?

What kind of test did they do on the alternator? Did they load test, or just check the output voltage . You might ask them to check it again, this time turn on the ac, blower motor on high, headlights, and anything else you can. Electrically, the headlights should have nothing to do with the charge light , unless the bright lights are loading the alt. more than its putting out. Check that all of the plugs on the back of the alt. are plugged in tight. Dont know what year it is, but most will have 1 wire that is single, the stator wire. This is what turns the light off, when the engine starts, and the alt starts charging. If the indicators are one on top of the other, sometomes a crack in the plastic somewhere, or loose bulbs will let light shine through to another indicator? Mine does that, one is right above the other. Good luck
Later
Ed

[armstrong]

I have had several alts and batteries tested before at parts stores and I have found it better to have them test it outside while it is attached to the vehicle so you can be sure you are running a load through them instead of actually removing the part and taking it in. I have had several batteries and alternators that they have tested and said were good but were actually bad. Also before you do that I would check all of connectoins like unclebubbles posted. Good luck.

[skeetyskeet]

They did output test, will have them check again and see. I'ts a 1997.
Thank you

[skeetyskeet]

You guys are right, it is alternator, thank you very much.