I had discussed this before but no real conclusion. I would like to use my auto headlights but in auto mode they are always on no matter how I adjust the knob on the mirror. They worked when I got the car but no longer function properly.
Does this mean I have to replace my mirror?

 

I would say yes for initial perspective, but it could be the dial rheostat and a local electrical shop may be able to meter it and replace for a 1/2 of the cost of a used one or replacement NOS (new old stock) mirror...if you can find one?

This site says its not in stock, but you have a part # at least ...Jaguar Rear View Mirror W/Auto Dimmer Xj8, Vdp, Xjr 98-03. HNC3133AB - Jaguar Parts Specialist ...another source you can try contacting is Dave... https://shop.everydayxj.com/Default.asp

I would also check The Marketplace here on site in the top task bar. I was skimming about a couple weeks ago and there were a couple cars being parted out.

This site has surprised me on availability in scrap yard searches... Car-Part.com--Used Auto Parts Market