Battery light my car start but then the battery light goes on.

but when I turn the key the radio goes off and ??? When you turn the key to start ? Do the dome light's dim ,the instrument cluster lights go off or dim ? Battery , battery connections , battery cables . Voltage drop test the main battery + an ground cables .
Starter Voltage Drop
The Trainer 47 What measuring voltage on the ground side means

Check the second battery in the back, under the subwoofer.

the IC on your alternator might already be busted

Yes, even though the battery might have enough power to light the overhead bulb, it may not have enough power to turn the starter.


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FGTech Galletto 2-Master EOBD2 V51 BDM-TriCore-OBD

If you disconnect the negative battery cable and connect a 12V test light between the battery negative post and the negative battery cable terminal the light will burn if there's a draw. Make sure all electrical consumers are off and all doors closed when doing this draw test. If the light is on start pulling 1 fuse at a time until the light goes out, when it goes out that's the circuit that has the draw. Trace it from there.

may be a bad alt check voltage while running should be about 14 volts

Check the alternator while the light is on. Make sure the belt is not slipping.

Have someone check the alternator for you.

sounds like a faulty starter engine. works sometimes, sometimes not. after some time will stop forever.

also check the vehicle's battery, see if the battery is charging normall , low amperage in the battery will be a probem too.

Check the charging system your alternator may be going bad or nOT charging fully. when vehicle is off the voltage at battery terminals should be at least 12volts and when vehicle is running at idle at least 14 volts. If this is NOT so when vehicle is off then battery is BAD. If NOt so when vehicle is running then BAD alternator. Also check battery terminals and make sure they are tightly secured and NO corrosion on terminals. Good luck and thanks for using FIX YA