'87 Syncro Westy.  Water tank has level sensor set up
as four screw probes in the tank.

The level lights work perfectly--EXCEPT for one case.
Green works, red works, but YELLOW only works for
a while, then changes to red.

If the panel switch has been off, then the yellow would
stay on for several minutes, then go to red.  But turning
the panel off, then on after a few seconds or a minutes,
and it would jump to red right away.  I was thinking it
was some component at the panel that warmed up and changed
behavior.

I removed the screw probe, cleaned it, filed it some,
checked all the connections and reinstalled.  Now the
yellow will stay lit for many minutes, then go red.
If I reach into the tank and touch, rub, etc, the probe,
yellow again for a while.  But eventually, after an hour
or so, back to red.

If I add about a teaspoon or so of salt (iodized) to the tank,
then the yellow light stays on, NEVER going to red.
So, I guess I could always add a little salt to the tank....

Also, I checked the ground connection.

It appears to be a conductivity problem.  Boulder water is
pretty pure and soft--not many minerals in it besides some
rust.

But what goes on in that flat, black, surface-mounted box
that the probes connect to?  Could it be something there.

Looking for experience with this--or electronics wizardry!
[It's my first and only Westy and I'm a software guy....]

Richard