I noticed that the charging light on my Explorer stayed on so I checked the running volatge at the battery. It was only about 11.6V. I know for a fact that the alternator is working because it has been tried on another vehicle. I have no idea where to start looking for a problem. One thing though, I noticed that the running lights both stayed on fine, but when I turn on the actual headlights, the drivers side light goes off completely. Another thing, although it may be unrelated, the vehicle lacks alot of power when going up hills. I probably just need a new fuel filter though. Any ideas?