Fuel lines to the fuel injectors leaked.
Transmission kick-down switch stuck, so car would not leave first gear.
Brake light switch faulty.
Short circuit in fuel injector wiring loom, no power and car towed home.
This car was the classic one old lady owner car. I have spent the last year giving it a very thorough overhaul - at this age, many of the rubber components of an XJS need replacement - e.g. fuel hoses in the engine bay, the wiring loom to the fuel injectors, flexible brake lines, coolant hoses, etc.
I would recommend one of these cars to any enthusiast who is willing to learn about the car, join a good forum, and perform their own preventative maintenance to some extent. Spare parts are reasonably priced and widely available. If you get everything done at a garage, this car could be very, very expensive to run.
If you put in the time, this is an amazing car to own. It turns heads like no other, the response from other motorists is amazing and universally positive. It's hard to think of another car from the 70s that still looks so fresh.
On the driving front the car has surprisingly modern road manners, with good brakes & safe handling. The only downside is the fuel economy, which is horrible around town (11mpg US) but more acceptable on a long run (17-20). This is thanks to the HE head design, optimised for cruising economy.
The main problem with XJ-S ownership is that you will fall hopelessly in love with all things Jaguar, and never have any money, or time, again.