Checking operation of the trailer hitch socket 1. Connect the test cable to the trailer hitch socket on the vehicle and lay the cable to the front. Scheme 1 Log in Scheme 1: Checking operation of the trailer hitch socket See also:• 39 90 55 Changing oil for transfer box - as of MY 2003 (All Models)• 85 15 19 Removing and installing heater/air-conditioning unit - as of MY 2003 (All Models)