Aftermarket fuel level gague

probably a warning light at the pilot box between the meters.
the 81/82 US 750E pilot assy has from top to bottom:

yellow turn signal indicators.
green neutral light & blue high beam indicator.
red oil light & red fuel warning.

fyi. the 1980 E1 meters have a volt meter on the pilot assy and oil warning light on the tachometer. no fuel level switch in the tank so there isn't a low fuel warning. 

Thanks for the information this really helps my dashboard was missing most of the letters . I dont have a voltmeter so I guess it's not the 81