AN AERO COMMANDER 500B MADE AN OFF ARPT LNDG DUE TO INADVERTENTLY CLOSING BOTH ENG FUEL SHUTOFF VALVES.

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WHILE PERFORMING AN INITIAL ACFT CHKOUT; I (CHK PLT) ASKED THE PLT I WAS EVALUATING TO PERFORM A NO FLAP LNDG. TO SIMULATE THE LOSS OF HYD PWR AND ENSURE PROPER LNDG GEAR EXTENSION WITH THE EMER SYS; I TURNED OFF WHAT I THOUGHT WERE SIMPLY HYD SHUTOFF SWITCHES. I HAD PERFORMED THIS SAME TASK IN ANOTHER AERO COMMANDER THAT I'D BEEN FLYING MANY TIMES BEFORE; AND HAVE NEVER SEEN ANY MENTION OF WIRING OTHER THAN A SIMPLE DIRECT CONNECTION FROM THE HYD SHUTOFF SWITCHES TO THE HYD SHUTOFF VALVES. AS I CHKED THE HYD PRESSURE AND BEGAN BLEEDING OFF RESIDUAL PRESSURE; WE EXPERIENCED A LOSS OF ENG PWR. I IMMEDIATELY RETURNED THE SWITCHES THAT I'D THROWN TO THE 'ON' POS. I ADVISED THE PLT BEING EVALUATED THAT I SUSPECTED THAT THE SWITCHES WERE ALSO WIRED TO THE FUEL VALVES AND THAT WAS THE REASON FOR THE LOSS OF PWR. AS WE VERIFIED THE ENG THAT HAD FAILED; THE OTHER ENG FAILED AS WELL. NOT KNOWING WHY THE ENG PWR HAD NOT BEEN RESTORED BY REVERSING THE SWITCHES; I DECIDED WE SHOULD CONCENTRATE ON MAKING A SAFE FORCED LNDG. BOTH PROPS WERE FEATHERED AND AN UNEVENTFUL LNDG ON A HWY NEAR THE ARPT WAS ACCOMPLISHED. WHEN WE INVESTIGATED WHY THE ENGS HAD QUIT; WE FOUND THAT THE HYD AND FUEL SHUTOFF VALVES WERE CTLED BY THE SAME SWITCHES; AND THAT THE SWITCHES HAD A PLACARD 'EMER SHUTOFF HYD AND FUEL CTL;' WHICH WAS SOMEWHAT OBSCURED BY THE SWITCHES THEMSELVES WHEN VIEWING FROM THE R SEAT. WE ALSO DISCOVERED THAT THE SWITCHES WOULD CLOSE THE FUEL AND VALVES; BUT WHEN THE SWITCHES WERE TURNED BACK ON; THE FUEL VALVES WOULD NOT OPEN UNLESS THE 3 POS (OPEN/OFF/CLOSED) FUEL VALVE SWITCHES WERE IN THE 'OPEN' POS. DURING THIS INCIDENT; THE FUEL SWITCHES HAD BEEN IN THE 'OFF' POS THROUGHOUT THE FLT.