How do you open the gas door in a 1977 Mercedes 280 E is there a switch to do open it inside or does it open from outside?

Press on either the RHS or LHS (I can't remember which) of the gas door and it will swing out and open - its a simple hinge system - no locks or latches. Good luck!

Actually: Make sure all the doors are unlocked, otherwise it wont open. Also, its the Left-hand side, not right.