Hmmm... That's cause for concern. Normally when one troubleshoots a problem like this it is just a matter of finding out what has changed between when it was working and when it was not. In this case the cause may be more insidious. I hope for your sake that it is just the alternator or voltage regulator because phantom current draw can be a real pain in the @$$ to try and troubleshoot. It goes something like this:

• Disconnect negative battery cable and pull all the fuses. Place a voltmeter (or ammeter of sufficient sensitivity) between the battery and the cable. Make sure there is no reading.
• Re-install fuses one at a time until the meter registers voltage.
• Break out schematic diagram and start tracing it back.
• Lather, rinse, repeat...

Any halfway-knowledgeable shop should be able to test the alternator output for you in about 30 minutes.