Do you know what type of alternator you have. I think it is the 12 SI series. Or it might be the CS style. If it's the SI series then you can check the wires on the plug that plugs into the side.
There are 2 wires to the plug and they connect to the no.1 and no.2 terminals.
With the key off the wire to the no.1 terminal should have no voltage on it. When you turn the key on you should have 12 volts on this wire. The other wire should read 12 volts all the time key on or key off.
Here's a picture of the SI alternator.
