I have a 1990 sovereign and i love it. Prepare to do work on one if you buy it though, especially if yours has the hydraulic self-leveling system. I have yet to find one that age that doesn't leak green hydraulic fluid all over.
5 inch speakers in the 96 Jag XJ6
Alpine
Traditionally the engine computer for a 1990 Jaguar xj6 is located in the car near the engine. The computer can also locate behind the dashboard near the engine.
Dexron III
R134a freon......
Drivers Door Jam On A Sticker It is also incorporated into the VIN# which you can get at any Jag dealer
the battery for your jag is in the trunk right side
Buy a Haynes manual at any auto parts store or online. It has all the wiring diagrams and fuse charts in it.
mine is a 92 xj6 and in the car handbook it has all the stuff jaguar reccommend. but i use castrol high mileage.jaguar reccommend castrol products.
Its in the fuel rail at the end of the head after the last Injector.
most likely the CRANK POSITION SENSOR
Buy a manual and figure it out an if you can't call a jag machanic to do it for you.