Hit failing alternator with a hammer to confirm diagnosis of failing alternator due to bad brushes
Hitting something with a hammer often feels good but does nothing useful. Here's one case where it actually helps. On my 2004 Ford Explorer the alternator light came on. I brought it to the auto parts store and they put a volt meter on it. The alternator needs to put out a voltage that is higher than the battery's full charged voltage in order to properly function - somewhere in the 14 volt range. Mine came in low - probably below 13.5 volts. So the guy at the auto parts store took a rubber mallet to the alternator and just briefly, for a period of 10 seconds or maybe less the voltage jumped up into the normal range before falling back to where it was before. This confirmed the diagnosis of a bad alternator in general and worn brushes in particular. The brushes are spring loaded, are located in the are a wearable item and must make contact with the fixed part of the alternator. Tapping the alternator with the hammer temporarily changes spatial relationships between the brushes