Next measure the voltage on the two small terminals on the back of the alternator, again, while the engine is running. They might be two wires that are plugged in or they could be two small nuts under a black plastic block that the wires go into. One will have full battery voltage. The other one is the key. It is supposed to be less than battery voltage but not 0 volts. If you find 0 volts, the brushes are open. If you find the same voltage on both terminals, either the voltage regulator circuit inside the Engine Computer is defective, (pretty rare), or the wire going to it is broken. If you find around 4 - 11 volts, that part of the system is working. There could be a defective diode in the alternator but I don't think that will turn the warning light on.
Monday, March 7th, 2011 AT 2:51 AM