2002 XJ8 Alternator turned on 3.45V with ignition off energizing the rotor

[Malcolm_J_Ives]

3.45v feed to alternator with key off?

[Neil_Maldon (Neil Bennett. Patron)]

Sounds like a welded relay or a s/c FET.

Check:

http://jagrepair.com/images/AutoRepairPhotos/jagxj2002.pdf