Disconnect the battery, if it's still flat after a week it's no good, if not flat, at least you know it's a drain, then do as said pull all fuses, inserting back one at a time to narrow down the naughty one, what size battery do you have ?, flat post are still made by two factories, try a conditioner/charger on the battery, these work a huge amount of the time to revive batteries to what they should be.
tabetha