Sounds inconclusive to me. The alternator should be full fielded with the regulator disconnected to see how many amps it's capable of putting out. A good tester machine will have an amp probe. It can be used to see how many amps certain componants are drawing when used, like the headlights. I once had another Ford that had a bad dimmer switch. It affected the headlights, but i'm not sure if the Mavs are grounded thru there or not. Maybe you have a headlight switch problem
Ive had the same problem w/ headlight draining battery before (was the switch also) If they didn't disconnect the regulator, they didn't help you out any at all. I've had alternators die the same day I put them on and they tested good. Yours still could be bad, but work at an idle, just not at higher RPM, or it could be the regulator as stated above. Just out of curiosity, is your alternator belt tight?
belt is tight, all seems to be fine now. i have driven it with the lights on and everything, but now the alt. light stays on all the time. fires right up without a problem and stays running though.
Try doing this: disconnect the battery wire at the alternator and connect a light between the wire and connector on the back of the alternator. If it lights up then you have at least one of the six diodes blown. Time to replace the alternator.
I would recommend a tail or brake light in a used socket. That way it is brighter than a test light and it takes more power to make it work. Either way if there is enough current to light a lamp you have a blown (shorted) diode. That will drain a battery fast!
today i hooked up an actual tester to it and found out the battery is fine, but the alternator or the coil is bad. so im soaking some bolts with pb blaster so i can get the alt. off and replaced and im going to go ahead and get the coil too depending on how much it is.
I've seen it happen, but not on a factory setup. Only when the wiring has been messed with and theres a short in the power wire or its on all the time
