How do you mount rear view mirror jaguar xj6?

Depends on what year the xj is and if your talking outside rear view or inside. I just replaced my inside rear view. It's auto-dimming. If it's the inside and auto-dimming, there is a cap on the top of the mount. Carefully pry back near the top and this peice should come off easily. You should then be able to push the mirror post straight down to release it from the windshield mount. Then you'll have to loosen the overhead console. Do this by using a straight blade screw driver to turn the plastic keeper screw, that is is visible with the sunglass holder open, 90 degrees counter-clockwise. Pull gently, slightly downward and toward the rear of the car. The overhead console is held in the front by two metal tabs so there are no more screws. That will free the overhead console and you can see the wiring harness for the mirror toward the front of where the console was. The connector has a tab so very carefully lift the tab and pull apart the harness. Re-attach in reverse order and you'll be seeing things in the rear of the car again! Hopefully not flashing lights!