Which TV series theme song was performed by a member of the group "Chicago"?

Peter Cetera Co-wrote and performed "Save Me," which was the theme from "Baywatch" (1989) during its maiden (network-based) season.

You got me there ,Bedstor and I must admit that your answer fits the question, not what I had in mind though.

The theme I am looking for bares the same title than the TV series itself.

Hint?? In this series both the Dad and son were performing together.

#2 clue, both have passed away- Son before Dad.

I will give the answer I was looking for.
In the heat of the night sung by Bill Champlin of Chicago.

You can hear the theme here
Hugh O,Connor bio son of Carrol O'Connor.