I have a T50TLR Yamaha outboard motor and its over charging at 14.8 I changed the rectifier and put in a new batterie and checked all wiring and still does the same thing any ideals.

Ahhh Mercury electrical... always a problem. The charging system on a mercury is really simple. You should have 2 yellow wires coming from the under the flywheel and possibly a black one running with them. These are high voltage a/c. They run to the rectifier/regulator which converts the a/c to d/c and sets the voltage to around 14 volts. To test the charging circuit, disconnect the yellow wires from the rectifier/regulator, *CAUTION HIGH VOLTAGE!* hook up a meter, set to read a/c volts to the two yellow wires and crank the engine, be careful not to touch the wire ends while doing this, it could be a shocking experience. You are just looking for any voltage above 12 volt a/c. If you start the engine during this test you could see upward of 100 volts. If this test fails replace the charging coil under the flywheel, it the one with the yellow wires that you just tested. Chances are this test passed with flying colors.So plug it back in and test the rectifier/regulator. Disconnect the red wire(s) and set your meter to read > 12 d/c volts, there may be 2 red wires. Start the engine and test from the red wire(s) to engine ground, you should see >12vdc. 99.9% of the time this test fails. So replace the rectifier/regulator. It is the weakest link. They will fail for something as simple as a loose or corroded battery terminal.

If its an outboard it is probably the rectifier. If you hooked up the battery backwards it will have blow the rectifier. You can check you should have AC coming off the yellow wires and dc coming off the red wire and ground. If your tach does not work that may also indicate a blown rectifier.

Bring it to a certified Yamaha mechanic

Disconnect the wire connections and OHM them out to ground. If you have a short to ground the wires will melt.

You should install a rectifier/regulator.
It's a small cast aluminium block, with a 4wire-connector:
2 to the charging coil ( where you measure 2*7volts ) 1 to the frame ( black ) and 1 wire to your main circuitry ( red )
You can take it from any 12v motorcycle. Sometimes, the aluminiumcasing is the ground ( no black wire ). Check that you allways have a good connection to the frame ( grounding ) in both cases.

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

Check your rectifier. Follow alternator wire, you will find a small probably square device. isolate it. Test it with diode checker or ohm meter. electric should pass one way but not the other. There will probably be two diodes in the device - one or both could be shorted (pass either way or neither way) Id check it before plunking down the $ for a new one. Could be your alternator is not putting out. Is your battery fully charged? No power into the alternator = no power out of the alternator. Alternator shorted - well time for a new one. Though this is not the weak link in a charging system. Could remorely be the voltage regulator ... still id look ata the rectifier.

Your motor is fine. It needs to put out more than 12 volts or the battery will not charge. Most alternators put out between 13 - 17 volts, so this is well within the range.