Had a similar cable connection in my unit. The little black button was for a signal booster as I recall. The round hole is a 12 volt outlet......like a cigarette lighter outlet but for plugging in a cell phone or ?? The red light should illuminate when the black button is pushed.
Have since changed it out when installed a HD antenna with a different switch plate.
2012 Fun Finder XT 276 Toy Hauler & Harley Davidson Ultra Classic with Condor wheel chock
2014 Dodge Ram 2500 AT 4X4 Crew Cab 6.4 L Hemi, 373 gears, tow package, Rambox option, Revolver X2 tonneau cover, Equal-I-zer anti-sway hitch.