No.1 wire is ground if the alternator quits charging. If the alternator is charging it could have 12v on it. Leave it disconnected or check the color (assuming there is some wire harness) and see if you can trace it back to the idiot light. You might be able to work from the idiot light to the alternator. A factory wiring diagram would be helpful. If you can trace the idiot light wire reconnect.
Larry
