went through all the switches and connections on the door after removing door card, everything seemed ok, no cuts or corrosion. I pulled the headunit out, it is the original with the front screen heater switch integrated into the unit and firstly removed the switch and no drop. when i disconnected the headunit it dropped down 0.2. I bought it the car from i guy i work with and he said that in the 3years+ he had it the head unit was never removed. the wiring looks original. can something inside be causing it to pull that much from the battery and basically mean that the unite itself is knackered??