Welcome. I will try my best to help you and in order to do that, I need you to describe as best you can because I only know as much about your problem as you have told me in your post, so my answer will be based on what you have posted. Please feel free to reply as needed.
Is there power to to either tab on the window?
There are three tabs on the read window, one on each side and one at the top near the middle. The two tabs at the side read 0.4 ohm zero resistance to ground (latch bolts on rear door). With power on there is zero voltage on these two tabs.
The top tab has a wire coming from under the roof covering and is completely covered. There is no metal contact to get a voltage. The tab is ~ 1/2" round and is made of plastic (rubber). I've tried to gently pry the rubber from the window (maybe the contact is a snap). I can rotate the plastic about 90 degrees with a little play in the wire. I haven't been able to get it off and don't want to pry too hard. I don't know how the wire actually attaches to the contact and I don't want to break it.
It's nice to know the radio antennae location, but the question is why doesn't the rear window defroster work.
There is no voltage to either tab on the sides of the rear window.
It has been found in some cases that there may be a terminal concern at C200/X200. Inspect terminal D6 circuit 293 for being fully seated in the connector and for proper terminal tension. If necessary you may bypass the connector for this circuit if a concern has been found. If there are no concerns with the terminals in C200 continue with the diagnostics in SI.
Location of C200/X200 is: Body wiring harness to the instrument panel wiring harness, behind the right front kick panel, below the instrument panel fuse panel.
Sir, you are too quick to give neutral feedback. I was not done.
Behind the right kick panel is the connector, #11 in the picture below.