u got to remember wot electrical stuff is used when the ignition is off as everything goes through that switch near enough
alarm / immobilizer / amp for sub / radio / courtesy lights / main lights / hazards / rear head light when indicator is on but ignition is off
also take the facia out and check the cables for volts on things such as the heater, ciggy lighter
u tried getting a volt meter on the starter motor & alternator as they pull some power
also u got the little earth box on veccy b's top right hand corner of the engine bay next to strut [little black sort of cover ] - it has 3 or 4 earth connections
if you can physically see your volts going down on the battery, ie like tenths of a volt every few mins then i would take each earth cable off and see how u go