The car: friends 96SE w/manual climate controls (Not A C C)

Problem: The Rear defrost does not turn on. The round push button to the left of the fan *** will not light up indicating that the rear defrost is working.
All I hear when I push it in is a click somewhere behind the dash, probably the relay.
I did check the rear defrost fuse and it is not blown.

So, let me know what to check next.
Thanks for your help w/this.

Todd