Now refit the contact strip. The plastic base fits into two small locating slots near the front. Make sure that all 6 contact points sit on the flange edges before pressing it into place. They can slip behind the wheels. Use tweezers to straighten the tabs which support the contact strips if necessary - they should protrude horizontally from the main copper strip. I'm not sure what the two tags near the gearbox are for. When in position, screw down the circuit board - as always, insert the screw in the board and offer both up to the threaded hole. It saves trying to fiddle with big fingers and tiny screws in tight places.