Water tank gauge on 330 express

[jip40]

I have the same problem & interested in accessing the back of the gauge

 

[fsc60]

I have an 01 330, I added a sender and gauge to my boat. I used KUS. This is what Grady uses now. I have it powered from the fresh water breaker. Put gauge in the head like Grady does. There is a link below for the sender. Their web site also has a trouble shooting page.
You can access the gauge by removing the control panel for the holding tank.

SSS/SSL Sender - SAE 5 Hole Pattern Mount Level Sender | KUS USA

This is our SSS/SSL electric liquid level sender. It mounts with a standard SAE 5-hole pattern. It works great with our industrial and marine applications.

kus-usa.com

https://kus-usa.com/resources/troubleshoot-fuel-level-sender/

 

[seasick]

KUS bought WEMA a few years ago.