Door Mirror / Heater Switch on 2004 Elegance 2.0TDi

My door mirrors no longer heat. I asked the garage to investigate while they had the car in for rear discs & brakes. Unlike other postings on heated door mirrors on this forum, the garage identified that I needed a new switch as well as one new mirror glass for the small sum of £140 including fitting.

Courtesy of this forum, I've gained access to the switch and checked the contacts. Assuming the pin that it uppermost in the installed orientation is Pin 1, then on the heated setting, Pins 4 & 5 are linked, all others open circuit. In the absence of a wiring diagram, I'm unable to establish whether this is what is expected. Can anyone advise please?

Also, the rear parking sensors are exhibiting the "long beep on engaging reverse gear" with then no display of car on the Stream Radio and no warning beeps whilst reversing, then the display of car on the Stream Radio appears briefly (~1 second) on return to neutral. I don't think this fault started on return from the garage, but is it possible that something associated with the garage work has upset the parking sensors - or am I just having a run of bad luck?

Many thanks

Andrew