There are three LEDs installed for that filter, Green, yellow and red, to let you know what mode you are in. Either bandwidth (green led) or center frequency ( yellow led). Selecting which mode you are in is done by pushing in the encoder. The red led is over drive warning when the input signal is too high, over 1.5 volts p-p.
These filters are easy to install and the unused header on the front of the main ubitx board is an excellent place to pull the input from, as well as grounding for the filter. Five volts for the board is taken off the 7805 regulator.
One comment on these variable filters. Not knowing where your center and bandwidth are set is somewhat of a pain. The extra nano and display, in my opinion, would be the way to go. I have yet to incorporate that.