What is the canister that sits near the alternator and has two wires going to the alternator. on my 1997 jag. XK8?

 

Noise Suppression Module ( 220000 uF capacitor , there is a old term I can't remember )

https://www.avweb.com/news/maint/182896-1.html

Same circuit as on the X300

The way you test it is with a digital meter climbing resistance , you can short it out and watch it climb again

What are you trying to resolve ?