Replacement glass for the Grand Cherokee side mirrors is available from Mopar, you do not have to purchase the entire mirror assembly. The mirror assembly does not have to be removed to replace the glass.
The mirror glass on the WK snaps in place by way of 8 plastic tabs and receptacles. To remove the glass, push the mirror glass fully inward towards the vehicle as far as it will go. With a pry tool (or large flat screwdriver with a shop towel wrapped around the end) carefully pry out the glass assembly starting on the lower outside corner. Once one or two of the tabs are popped free you can pry the remaining tabs apart from the housing using your fingers. Unhook the electrical connectors from the glass assembly.
To reinstall the glass, connect the electrical connectors and then carefully center the glass assembly evenly onto the circular base of the mirror housing. You can peek behind the glass to make sure you have the tabs lined up. Then press firmly, going around the center area of the glass to snap in all 8 tabs. By hand, move the mirror back and forth in the housing to center it horizontally and vertically. Check to make sure it is installed correctly, it should be flush around the housing on all sides. Check proper operation with the power switch.
Mirror assembly removal
1. Partially remove the door trim panel as necessary to gain access to the mirror mounting area (see Front door trim removal ).
2. Disconnect the wire harness connector from the mirror.
3. Remove the three nuts that secure the mirror to the door and carefully remove the mirror.
Underside of Grand Cherokee side mirror. 1999-2004 mirror shown, 2005-2010 mirrors are similar