Antenna adapters

Hello dear Audi community,
I am the Christian and come from the Mainz district. My Dicker is an A8 D2 from 1997, 4.2l V8.
Of course, I have a few questions:
Since the extendable antenna has always annoyed me, I want to exchange them for an antenna foot with thread for an external rubber antenna. I took the foot from the year 1999 of a D4 and fits also so far, but the plug does not fit on the internal installed antenna cable. Is there a specific adapter for this or do you have to make something here yourself?
Then I found a kind of compressor on the antenna side over the wheel box with 2 green hoses during the removal, which always makes noise when I open or close the car. Don't have air suspension or level control, what kind of task could this thing have?
I would be grateful for one or two answers and hope someone here knows advice.
VG
Christian