power drain

Hi all, My s320 cdi has a power drain, I have managed to trace it to one fuse, its in the rear drivers side floor box and it controls the radio, nav, phone and central locking so its a bit of a pain to leave it out. The drain happens over a day or so and its not too handy as i have a wife...

My new battery has died for some reason but I cant get into the boot to charge it. Iv tried the key blade in the boot lock it turns fine but wont open.