Black water tank sensor wiring

[Creek Jenkins]

My 2/3rds light on the black tank level sensor does not work. The light does come on for the grey tanks and fresh water tank levels.
I am hoping it is not a problem at the tank. I pulled the wall panel and found a green wire coming out of the circuit board that runs the sensor lights not connected to anything. I cannot find another unit connected wire. Anyone else see this?

 

[fireman0175]

Do you have a red or purple wire to your panel for sensor lights? typically, the green wire for 2/3s goes to a common sensor wire I have read. Do you clean your tanks often as they are famous for not reading correctly.