Sorry it took so long to get back on this thread, I got my mustang running again.
So the alternator was definitely to blame.
The part number I got was SUM-810301 , identical to the one in the OP
Summit racing could only give me 20% a new alternator since my warranty was up so $110 later I had a new one. I stuck with the same one this time. (and final time if this one dies)
With 4 ga wire at both the positive post and the ground post of the alternator i was pushing 13.8 volts at both the battery and alternator at idle.
So the alternator was definitely to blame.
The part number I got was SUM-810301 , identical to the one in the OP
Summit racing could only give me 20% a new alternator since my warranty was up so $110 later I had a new one. I stuck with the same one this time. (and final time if this one dies)
With 4 ga wire at both the positive post and the ground post of the alternator i was pushing 13.8 volts at both the battery and alternator at idle.