My Avian fan transmitter is wired but need to know what black wire ith tape is for. Aground or to transmit

What other color wires do you have..?

A "Black" wire with tape? My guess is that there is damage to the black wire.

If it is a White wire with black tape on it, it means (most often) that the White (Neutral) conductor has been re-tasked as a Hot conductor and is no longer a Neucral conductor.

Transmitter or receiver?

If it's what I think it is that is not tape it is heat shrink, and it is the antenna. DO NOT cut it.

I have to say it again, as I just did in two other threads, photos will help greatly.