Originally Posted by JimN
The check engine light goes on and doesn't flash, or you just see it flashing at a constant rate? You can't use a paper clip on your engine- it's not OBD I. You could use an OBD II scanner, though. Autozone, O'Reilley's and other parts stores loan them.
Are you close to any MC dealer? Call and ask if they have a diagnostic computer & someone who knows how to use it.
The OBD II and the CAN connectors are not the same and you cannot read codes from MEFI 5 ECMs without a CAN.
Normal automotive OBD II
Left to right:
Perfect pass adapter for CAN connector(used to hook to mefi 5 ecms when the boat has a PP), MEFI 1-4 diacom DLC connector, CAN adapter, Diacom cable.
OP, You'll need a DIACOM system to pull codes on your boat.