Low alternator voltage

Get a load test on both. There are 2 components to checking the system voltage and amperage. You can have good voltage but low amperage which will cause issues. 12.75v is low. A battery fully charged should be closer to 13.8v and charging should be around 14.4v

There are much better, safer ways to test the alternator. You should never remove the battery when engine is running or when the key is in on. That old style method was before engine computers. It causes voltage spikes which can fry delicate electrical components, the computer and its many low voltage circuits, and the alternator as well.

Use a voltmeter (costs like $20), and check battery voltage-a good battery should read at least 12.5 volts. Then check battery with engine running. A good alternator should show 13.5 volts at the battery. Then you know the alternator is working. If battery is still same as when not running, the charging system is not working.

It is just possible that you have a bad alternator. Take it off and have it tested at a parts store for free.

The ECU has no control on the voltage. Does your vehicle have a separate voltage regulator? If so that's your fault. A lot of alternators have the regulator built into them. The alternator needs to be put on a test rig away from the vehicle and the output tested, this will eliminate the vehicle, You could disconnect the wiring to the alternator, run three fly leads to the alternator and to a separate battery and run the engine and test the voltage on the spare battery. Wire 1: Battery neg to case of alternator Wire 2: Battery pos to + terminal on alt (the thick wire) Wire 3: Battery pos through a 5 watt bulb to the ind terminal (ignition light) 17 volt will blow another battery for sure.

Could you please explain in further detail what is the L wire you're referring to?

if you think alternator is putting out the proper voltage. then check the post on alternator for voltage. its a possibility, that the wire is bad ! coming from alt, to battery and starter. if vehicle is running, there should be at least 13.6 volts to14.2 at battery posts. the higher is better. its also another possibility that the fuseable link in wire has blown ! that goes to battery. good-day !

If all the connections are clean and tight at the battery it is likely. The alternator should put out about 14.2 volts when the engine is at a fast idle (about 1500 RPMs). Auto parts stores will test your alternator for free.

BATTERY LIGHT ON MOST LIKELY THE ALTERNATOR DONE.CHECK DRIVE BELT FOR TIGHTNESS CHECK BATTERY CABLES FOR CLEANESS AND TIGHTNESS.CHECK ALTERNATOR FUSE AND CHECK ALTERNATOR BATTERY PLUS FEED WIRE.MAKE SURE GETTING GOOD 12 VOLTS THERE CHECK FOR LOOSE OR DAMAGED VOLTAGE REGULATOR WIRES.

Was the old alternator tested to see if it was bad? If it was and all wires are in good shape and reconnected the new alternator the new one may be bad also. It can happen.

first check battery voltage. should be 12 volts or a little over. IF the battery is low then charge battery and then load test battery. If you remove you battery and take it to local parts store most will check for you. if battery load test good but was low on voltage then I would check to see that alternator is charging while engine is running. should be charging aprox 13.9 volts. if battery had full voltage and load tested good then most likely the starter is bad.