While the various year challenger convertibles were used extensively in the mod squad series as others have pointed out there were many more cool mopars that appeared in scenes or background.

What I can’t believe is that no one has made reference to the 1971 barracuda convertible that was in the show.

I don’t recall the name of the episode and only remember seeing it once. It’s a red barracuda convertible with a flat hood, black interior, boot and body side molding. It’s a minor vehicle as far as screen time but there’s a good shot of the car since it pulls up to a stop on the street.
In the scene a girl in a bikini is driving the barracuda pulls up along the street and gives a young boy a ride who’s going to the beach. If I remember the rest of the episode, Julie (Peggy Lipton) goes looking for the missing boy. Maybe that info will help someone identify the actual mod squad episode and year that it appears.

Here’s a picture of the car from the mod squad episode.