[Excaliber]

The regulator has to be powered up by a 12 volt signal to 'energize'. This signal usually comes from the ignition switch and is generally wired through the 'red light' on the dash. No red lignt ON, then no power to the regulator. This step is often missed, checking for power to the regulator. A jumper wire can be rigged up to bring 12 volts to the regulator for testing, but you have to know WHICH terminal to energize to 'turn on' the regulator.

While it sounds simple, and it is, it is often not understood or overlooked by even a good mechanic.

You don't have to have a 'red light' (charging indicator). Sometimes a resistor is used in it's place, but a bad resistor or connection will result in a 'no charge' signal is given to the alternator FROM the regulator. In this case replacing the regulator and alternator and battery will NOT solve the problem. Testing each component will show them to be working well, so that won't solve the problem either!

Alternative test is to bypass the regulator, this often leads to incorrectly assuming the regulator is 'bad'.