Sedan Model

WARNING: This page is about a different car, the 2012 Subaru Outback and 2012 Subaru Legacy. However, it is still accessible from the selected car via links, so may be relevant.

Disconnect the ground cable from battery.
Remove the rear shelf trim. Refer to REAR SHELF TRIM .
Remove the high-mounted stop light.
1. Disconnect the connector.
2. Remove the lock washers and remove the high-mounted stop light.
  
  Fig 1: Locating High-Mounted Stop Light Connector And Lock Washers
  Courtesy of SUBARU OF AMERICA, INC.