There is an excellent post by JSeery dated 4/6/2015 concerning gauge operation. After reading this information it appears to me the the gauge operation is unaffected by a change from positive to negative ground. Is this conclusion correct?
...when i changed from 6v to 12V on my 40 Ford the BATT gauge … I had to isolate the BATT gauge so it operates as a single gauge and use a 60 ohm resistor in series with the 12V input to the gauge so gauge will read properly.