Just got my 2005 XJR from the shop where new front struts were installed and now the rear speakers do not work. How do I fix this? Do I just buy another replacement?

 

Did they work before the struts were changed?
Have you checked the fader to make sure they haven't been adjusted to just play through the front speakers. Press the mode switch to bring up the adjustment controls.
It maybe an amp issue if both have gone at the same time, or something as simple as a dislodged optical cable or speaker wire.