Maureen Mccormick was in an episode of Happy Days called Crusin'. It aired on February 11, 1975. Just thought this was a fun fact.

http://tvtome.com/tvtome/servlet/GuidePageServlet/showid-270/epid-20509

This was from the great early Happy Days era - when they sometimes filmed outside. She played a girl Richie picked up when he was cruising around. She acted like she liked him, just to make her boyfriend jealous.

christopher knight was also on happy days called my valentine

Yep. I've seen this episode many times. It's a great episode.