What was found
WHILE IN A HOVER, DROPPING OFF A LOAD, THE LOW ROTOR HORN AND CAUTION LIGHT WAS ACTIVATED, FIRST INTERMITTENT, THE PILOT WAS STILL IN A HOVER AFTER ACTIVATION SO IT WAS NOT ENGINE RELATED. DROPPED OFF THE LOAD AND LANDED BACK AT STAGING. IT WAS A FALSE INDICATION. WHAT HAD FAILED WAS THE TACH GENERATOR. A SERVICEABLE TACH GENERATOR WAS INSTALLED A FUNCTIONAL CHECK WAS CARRIED OUT AND THE ACFT WAS RETURNED TO SERVICE.