What was found
AIR TURN BACK, DURING CLIMB OUT, THE CREW NOTICED THE LT FUEL QTY INDICATOR ACTING ERRATICALLY, SHOWING A RAPID DECREASE IN THE AMOUNT OF FUEL ONBOARD. AFTER LEVELING OFF, THE INDICATED FUEL LEVEL CONTINUED TO DROP, EVENTUALLY DISPLAYING ZERO, AT WHICH TIME THE FUEL LOW LEVEL LIGHT ILLUMINATED ALONG WITH A MASTER CAUTION. ELECTED TO RETURN FOR MX SUPPORT. NO EMER WAS DECLARED. MX DETERMINED THERE WAS NO FUEL LOSS. REPLACED THE FUEL QTY INDICATOR. ALL OPERATIONS CHECKED GOOD & ACFT WAS RETURNED TO SERVICE.