Any electrical item in your car that is not on or able to be turned on while the car is OFF is a possible source of accessory 12V.

The constant connection in some cars will sometimes have thicker gauge wire than the 12V accessory lines (for the previous poster). In my car however, the stereo accessory line is fused with a higher rated fuse (doesn't matter because both are far higher than what the empeg would ever draw - they're mostly for fire protection from shorts).

Bruno