Welcome Floppy
to the weird and wonderful world of XJS ownership
The wing mirrors and the ? just packed up, what else? Did they pack up at the same time? Did both mirrors pack up together? Are you sure they were both working? Wing mirrors can be very finnicky for several reasons but I'd go for multiplug connections in the door and the operating switch first. If you have something else that stopped working at the same time could be a fuse if you're lucky. I havent got a V12 manual to hand so cant advise what else runs off that fuse, but if you drop the fusebox covers off (above your knees both sides) the placards are pretty clearly marked.
Cruise control may well be the seals at either end of the bellows - in the mddle of the V on top of the engine, if these leak air no cruise control, you can remove the unit and reseal with silicone, but again may be an electrical problem.
Re heater - when you say it does not work, what exactly does not work? I presume when you turn the right hand control (fans) on nothing happens. Could be an electrical connection fault of some kind but my money would be that the fans have seized due to lack of use - has the car been stood for any length of time?
You should be able to tell if the temp control works anyway. When your on the open road at reasonable speed a little air gets through the system, so turning the control from hot to cold should affect the yemp of air coming into the car esp in the footwells. NB it will take a little while for the flaps to operate and temp to change, also I would pull the left-hand control towards you (manual) htus ensuring you get the extremeof the range. Right hand switch should beonie low, auto etc.
Areyou completely new to Jags? If so sorry if this all sounds over the top take comfort from the fact that the XJS is a GREAT car - I would say that wouldn't I? JEC Devon Region have lots of active members who I am sure will help and this forum has many owners with much experience of living with and loving the car, Im sure you'll get much good advice.
When you say you haven't a clue are you mechanically minded? I think its fair to say that running an oldish XJS whilst paying a garage to mend every fault can be a dear business. If you can atke easy bits apart and clean terminals etc it will save you a fortune
Nice to have you aboard and above all enjoy your car as you drive past the eurojap identikit boxes.
Regards
DH Dove