Do you plan on fixing this yourself? Parasitic draws are some of the hardest problems to track down. But unless you are prepared to systematicly attack this, it will likely be elusive.
An amp meter installed on the battery negative is required. Clamp on style is easier. Shut type is cheaper. Turn off all devices. Pull the dome light and the other courtesy lights. Record the amp draw. Pull the fuses one at a time from the central junction box (BJB) and record the amount that the amp draw drops. Some of the fuses will drop more than others. Post the results.
FWIIW if there are any after market sound systems are installed, the search should start with these.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.