If you're referring to the small wires on the back of the alternator, there should be voltage there for one second after turning on the ignition switch, then again during engine rotation, (cranking or running). The system can be diagnosed by measuring those two voltages while the engine is running. One will have full battery voltage. The other one must have less but not 0 volts. 4 - 11 volts is typical. If it's 0 volts, the brushes are worn. That is often intermittent so you have to check it while the problem is acting up. If you find exactly the same voltage on both wires, there's an open circuit between the second brush and the voltage regulator in the Engine Computer.
Also check for battery voltage at the output terminal when the engine is not running. If you find 0 volts there, the large bolt-in fuse in the under-hood fuse box is blown.
Friday, August 26th, 2011 AT 6:06 AM