What regulates voltage for mercury outboard?

It would depend on the stator used. On the 9 amp stator, a regulator is not used due to the low voltage output, this system has a rectifier only. The 16, 32, and 40 amp systems may use single, or dual regulators to both regulate, and rectify the current from AC to DC voltage. To determine which system you have, follow the two yellow wires down from under the flywheel, where the stator is mounted, to either the rectifier, or the regulator. Note: The 40 amp stator will have two sets of yellow wires connected to the dual regulators.