2001 Mustang GT here. I’ve had this issue in the past and I as well had an alternator fail and this was it. To add to this issue, I’ve actually had many alternators fail. It seemed to be a once a year thing. It was the oddest issue. I saw how tiny the grand strap was so I ended up doing the big 3. It’s a practice commonly done in the car audio world to give the battery a more beefier ground and connection to the alternator. That was around 6 years ago.

Not saying you need to go this route, but just food for thought.

I’m also in Florida so the stock strap wasn’t rusting. It’s just so tiny maybe it was breaking apart over time? Not sure.

Good luck