Now that I own the boat I am going to do a deeper dig in search of the interior end of the cable tv wire. I have found no sign of a slider switch or an extra wire. The PO put a new antenna on recently and he does not recall seeing it either.
He said to look under the settee and the back it might be there. If not I may have to run a new one from the cockpit.
For what ever its worth the cable hookup, for the dockside cable, is located under the starboard forward cockpit side where the 50amp power cord comes out assuming you have the Glendenning power cable system. If your Tiara didn't have the Telephone/cable option when built you may only have a cable going to the TV antenna on the hardtop....BTW most marinas around here have given up suppling cable TV at the pedestals and are now providing WIFI... I purchased a Camp Pro 2V2 WIFI system and it works great on my flat panel TV's.... You create a local wireless network on the boat.