charging light

If the charging light is on with the engine running the alternator is not charging the battery. Put a voltmeter across the battery at rest, the voltage should be 12.6 volts, now start the engine the voltage across the battery should be 14.7 volts approximately. Disconnect the plug at the back of the alternator with the engine off, turn on the ignition key to the run position one of the wires should receive power from the ignition switch to power up the alternator. The big heavy wire at the alternator should have Battery voltage all the time as it goes straight to the battery to charge it.