The most common way for these alternators to fail is to become intermittent due to worn brushes. It can easily test good, then stop working a minute later. You have to watch the charging gauge on the dash, then perform tests while the problem is acting up.
Battery voltage must be between 13.75 and 14.75 volts when the engine is running. If you find low battery voltage, typically around 12.0 - 12.5 volts, you need to measure the voltage on the two small wires on the back of the alternator. Those voltages will determine the next course of action.
Tuesday, March 9th, 2010 AT 1:02 PM