2004 mustang gt charging issue

Test the battery. Clean the battery terminals.

The alternator CAN NOT run without a strong battery. The days of jump starting a car with a dead battery are over. The battery is needed to excite the alternator field coil.

Bad-battery=low/no alternator output.

Once the battery and terminals are good, clean, and tight, if the voltage is stiill too low, have the alternator tested at the autoparts store.

I am with wmburns on this one.

Couple of other things to try.

Test the load voltage on the batt when you start the car if it drops below around 10.5-11V then your bat is screwed. Also check the charge voltage it should be around 13.5-14V at idle.

Good luck!