Download 1991 Mercedes Benz 500SL Convertible Top Hydraulic Control Unit. The hydraulic unit (pump, motor, supply reservoir) is located in the spare tire recess. If the switch for the roll-over bar convenience feature or the switch for the soft top is actuated, the pump (A7/5) runs as long as the switch is pressed, pumping hydraulic fluid at a pressure of approx. 180 + 20 bar . The pressure is limited to 180 bar by a pressure limitation valve.