Reading this about the amp in the back i'd thought I better take a look. found a power lead about 8 foot long going to some sort of USB plug that was rusty and bloated, scotch blocked to the amp power lead, so that could be a lot of the drain (no fuse to be found anywhere). Next the towing socket....all scotch blocked again so this might be another source of the drain. Had enough for today so I ordered Tow bar bypass relay for Cambus vehicles. I'll see if I can do another test in the morning. ( I've also ordered the Car Battery Switch Isolator Terminal Quick Cut-off) Belt and Bracers