Rear wiper motor seldom fails and have you tested and confirm it is bad? Quite often the wires between tailgate and body breaks internally due to bending/flexing as a result of repeated opening and closing of tailgate over time.
1. Remove the rear wiper arm.
2. Remove the lift gate trim panel.
3. Remove the rear wiper motor bolts.
4. Remove the motor by sliding the pivot shaft out of the rear window grommet.
5. Disconnect the electrical connector.
6. Installation is reversal of procedure.