That is a TLM model. Go to this site and click on the right hand side box to download instructions.
GROCO TLM-10 uses simple and reliable technology (floats) to indicate tank level in fresh water or waste holding tanks.
www.groco.net
Does the holding tank macerator run when you press the pump out button? If not, that might mean that there is no power to the control panel or a bad ground. ( or a dead macerator)
You will see the instructions that if the system thinks the tank is less than 1/4 full, no lights will be lit. The sender in the tank can go bad or get stuck. In addition to often being hard to get to, the job can also be a stinky, dirty one.
Have fun!