Holding tank level indicator

Now I'm getting around to the real low-priority stuff :-)

As delivered (used), our indicator panel reads "E" until the holding tank is full, when it reads "F" (can't remember exactly what the panel says).

There are 3 terminals in the holding tank, plus a 4th wire.  2 are cut (probably the problem, but not sure why anyone would cut them).  I don't see all that many wires back at the panel indicator.

Does anyone have the schematic or general theory behind these indicators?  I'm thinking there are only 2 wires returning to the panel, and that the parallel resistance of the 3 terminals must result in different voltage?

I know dirty water is a better conductor than clean..........

Dan,

As an Elect Engr I will take a guess at what's going on based on what I remember on my fresh water tank...

You have these sensing points with a common 'ground' terminal.  As the liquid rises and touches each successive point, the slight conductance through the liquid is sensed and the appropriate LED is turned on.

Can't imagine why two of the terminals are disabled.  If you can find the wire inputs at the panel indicator you could try to reconnect.  It's nice to know before the holding tank is already full.

Ahhh, a fellow EE!

I found this linke useful:

http://www.gulfstreamcoach.com/tidbi.../Vol10No1.html