JamesW was a little vague in his suggestion. To verify that the electrical system is completely off and something is not draining your battery, disconnect the one of the cables at the battery and place an ammeter between the cable and the battery terminal. A test light will also work as well, a voltmeter can be damaged if the current draw is to great. If you have a current drain, aka - short, something is still on, a regulator related problem including the radio bypass condenser - you will see the ammeter's needle move, or the bulb in the test light 'glow' very weak. Pulling individuals fuses (alaJamesW)is a good next step, checking the status of your indicator, meter or bulb, with each removal. Remember,even ifafter all the fuses are pulled and theindicator has not changed, that means the problen is not in a fusedcircuit. You have circuit breakers to contend with.
I had a battery drain from the clock in my Rally Pac on a not to often used car. I put in a battery disconnect switch, it saved my battery. There's a disconnect switch on all my not to often used Mustangs now.
Jim

 

Yeah, my father-in-law has a 1980 Chevy El Camino , and his battery kept going down on him. Turned out to be a glove box light. A multi-meter is about the best tool in your toolbox.

 

im gonna have to get a new volt meter i guess. mine broke on me.