The helicopter had undergone an annual inspection and was preflighted and flown by the pilot for a maintenance test flight. The pilot did not check the right fuel tank level during that preflight. On the following day, the pilot and another pilot seated in the right seat departed on another maintenance test flight without visually checking the fuel level in either fuel tank. They instead relied on fuel consumption calculations based upon previous flight time and fuel gauge indications. After about 42 minutes of flight time, the helicopter experienced a total loss of engine power. The right seat pilot then performed an autorotation but had to maneuver to change the touchdown point in order to avoid power lines. The helicopter then experienced a hard landing. Examination of the wreckage revealed that a connector from the right fuel tank sending unit was disconnected. There was about one cup of fuel in the left fuel tank and no fuel in the right fuel tank. The helicopter sustained substantial damage, including damage to the tail boom. The left seat pilot received minor injuries and the right seat pilot received serious injuries.