Charging meter on the dash or the test bench?
Testing the alternator off the engine is not an effective way to test it. That overlooks the most common sources of problems in the system.
The fastest way to tell if the system is working is to measure the battery voltage with the engine running. It must be between 13.75 and 14.75 volts. If it is low, measure the two voltages on the two small terminals on the back of the alternator. That must be done with the engine running. One will have full battery voltage on it. The other one should have less, but not 0 volts. Typically you'll find 4 - 11 volts. If you find exactly the same on both, there is a break after that. Most commonly that is due to corroded terminals in the connector going to the voltage regulator in the Engine Computer. If you find 0 volts on the second wire, the brushes are worn inside the alternator. A nine-dollar assembly will fix that, or you can just replace the alternator.
The third wire is the large output wire bolted to the back of the alternator. That one must have full battery voltage all the time. If it is missing, there is a blown large fuse or fuse link wire. That can be caused by accidentally grounding the terminal with a wrench, but the more common cause is two or more shorted diodes inside the alternator. For that, the alternator and the fuse must be replaced.
Tuesday, March 21st, 2017 AT 7:26 PM