Hi Jim. Forget about it being a Jag, Think of it as a "CAR"

As Tony says, Check the charging, It sounds as though it is overcharging, Don't worry about charge Relays, It will simply be a conventional Alternator with a built in regulator.

Anything above 14.5V and you could have a problem, but I bet yours is going much higher when revved. ??

P,S How can you admit to not knowing about them when you have bought one to practise on. ??

Tony Sefton. Jaguar owners appreciation society.