> At Oshkosh last year the technical manager for tSandel came to my plane
to replace the unit with the show demonstrator that looked fantastic in
the booth.  After the installation he admitted that they have a little
problem.  He could not read the unit in the plane either.

Do you have a dedicated dimmer circuit for the Sandel?  It requires one.  
They may say otherwise, but the only way to get around this problem is to put
their dimmer on a dedicated circuit.  Read your install manual.