So I had the check engine light come on for p0345, was due for new battery, changed that out and the altenator at the same time. Now the battery light came on. Do you guys have any insight on this. Also 2005 mustang gt.

 

Test the voltage across the battery posts with the engine off and with the engine idling (no electrical loads). Let us know what you find.

 

Figured it out one of the wires going to the altenator was frayed. Cut the wire and replaced it with similar gauge and soldered it in. Battery light gone.