water tank level monitoring

[esf]

I have a 1996 31 Open and the level gauge does not read for either the water or waste tanks when I press the button to select the tank.   The light is on indicating power.   I do get an high level on my waste tank when it is full.  The original was a Fireboy Xintex Liquid Level monitor LLM-2 system.  

Does anyone have suggestions on what to look for?  Also looking for recommendations on replacement systems as the Fireboy is no longer made.   

Thanks