Pound to a penny your alternator has a leaky diode to earth causing your drain. quick way to check,switch everything off then lift off + batt lead then just touch it back on is there a sizeable spark?? then pull the plug out of the alternator or disconnect the heaviest lead from it then see if the spark is smaller or non existant, very crude check but works.
if you want to be really clever but cant read a meter get a 12v bulb and remove the + battery connection put one end on the batt + and the other on the lead you,ve just removed. take note of the brightness of the bulb whilst disconnecting various accessories, until the light either goes out or dimmer.
HTH
Alfie B