Quick update.
At the weekend i decided to find out why my passenger mirror does not heat up. Looking at the wiring diagram i noticed the wires split after the relay but before going to the doors. So to trace the wire(s) i stripped my dash down.
Starting from the fuse box.....
to the dash loom plug in the passenger footwell.....
I tested with a test meter to find cable is intact. After the green connector the cable splits and goes off to each door. checked the connector which links body to the door and that is working too so the problem lies with the cable within the passenger door to the mirror.
So job for next weekend is to strip door down and repair/replace door loom. (door connector male/female connector looks ok). What a pain in the rear!