Websters 3rd New International Dictionary lists "gauge or gage" under the
"gau.." heading. Under the "gage" heading they "see also gauge".
My 1988 GMC truck's warning indicator is "Check Gauges"; the owners manual
lists "gages" under the G section.
The description of the instruments ("Gages/Indicators") has an illustration
of the indicator. It's legend says "Check Gages" but the description along
side the illustration says "Check Gauges".
They really hedged their bet on this.