Red button behind carpet lining of trunk

I have a 92 500SEL and on the right side in the trunk by the intake pipe for the fuel there is a red button which looks like it could be depressed. What is this for? Is it a fuel shut off? Also can you tell me if this car has a hydrolic suspension and how would I test it to see if it is working properly? On my father's Lincoln there was a switch that turned off the automatic leveling system and I was wondering if there was a switch on this car which could have been turned off by accident. What are the symptoms of the air cushions going bad?

Thank You
Fred Berry