I don't know which season of Happy Days this next item comes from, but if you guys can help, I'd appreciate it very much.
Potsie (Anson Williams) performs a solo cover of the Shirelles' "Will You Still Love Me Tomorrow?", which was a huge hit in the early 60's.
Personal note: my high school sweetheart, with a lone guitarist accompanying her, performed this same song at our senior class talent show. Williams' version may or may not have been the inspiration.