Re: Nissan 30 4 stroke charging
If equipped with charging, the rectifier output appears on the battery cables. If you run the motor without any battery connected, you run the risk of burning out the rectifier. This is the case for most outboard charging systems. I would make sure the battery is properly connected, and check for charging by taking an ammeter reading.
If not charging, refer to the service manual (available from a dealer) for troubleshooting. The alternator itself makes AC; the rectifier converts it to DC for charging. You should also find a 20-amp fuse in the system, which can be blown if the battery has been connected backwards.
HTH