2001 yamaha 175 hpdi wont charge above 12.4v at high rpm. only 11.8 at idle. all connections to batteries are clean and tight, both batteries are good only some what discharged at this point from the lack of alternator? output.

You have two components for the charging systems. Stator and Rectifier regulator. As a rule of thumb we always change both. First you need to confirm that the outboard is not charging your batteries. use a battery load tester on your batteries confirm you have no dead cells. Second with a fully charged battery, multi-meter, and a water hose connected to your outboard cooling system. third for a picture and diagram of the ignition system go to www.yamaha-motor.com. click on outboard motors,parts and service, view parts catalog. find your year make and model by following steps listed at top. search electrical 1,2,3 until you find a RECTIFIER & REGULATOR ASSY. Click on generator to find the stator. when you find it you will have a picture reference. Check for good ground at the Rect/reg. the stator creates AC voltage the rect/reg converts to DC. rect/reg conects to the battery to charge it through a solenoid on the engine. Connect your multimeter to this solenoid to get the true reading from charging system. start engine check voltage through all rpm ranges. 13.5 v thru 15 v. The other troubleshooting test and disasembly will require a Manual. also to remove the stator you'll have to remove the flywheel.Clymer Service manuals are available through your local outboard dealer. good luck