Taking out the interior of parts car. Antenna?

 

Sorry, I had to write this: Looks like you have a JAGUAR walking with its paws over your backlite (=rear window)!? (...or maybe it's just the paw prints of another member of the feline species: A cat...)

And yes: Your "part" looks like an antenna cable - maybe an old remnant of a now disused "high tech" in-car-telephone, which was the latest technology had to offer back then....

 

Definitely part of the car phone setup. My now daughters 98’ XJR still has the entire car phone setup installed.

If you look close, you can see the coax hooked up on the left side.