Try contacting Merc tech support - I had an old merc 900 and they were able to answer my questions. Please come back and let us know what you find out, especially if they send you an operator manual.
Mercury outboard tech support is available through MotorGuide Technical Service1or Mercnet2. You can call MotorGuide at (920) 929-5040 M-F: 8AM-5:30PM EST or send them a message using this form1. You can also call Mercnet at 800.556.4327 or email them at mercnet.support@mercmarine.com2. Please have your product serial number ready