Hi Paul, I know from personal experience about electrical issues on these cars. Your best option , if you wish to avoid huge garage bills is to get an OBD2 reader and a multi meter. An OBD2 that will handle this sort of thing is about £50. A better one which will reset abs, airbags etc is about £250. Multi meter is about £20.
These combined with the wiring diagrams at jagrepair.com will solve all but the very worst issues. If you don't know anything about electrics, they are not as scary as they sound. There is loads of info and guides on the same website, but if starting from scratch be prepared to spend a lot of time getting used to all the jargon etc, but if you have these cars it will be time well spent. I have self taught myself and it is so worthwhile. Only yesterday my engine management warning light came on. An hour later all sorted using OBD2, multi meter and wiring diagrams. Turned out was nothing more that a sticky relay. Most electrical issues on these cars is bad connectors etc and nothing serious, usually free or very cheap to sort out if you take the time to learn.
In the meantime, if you study the wiring diagrams at jagrepair.com, if you list what is not working, there may be a common power source to them all, which will give you a clue as where the problem is. Good luck.
Peter