What was found
(CAN) CREW INTENTIONALLY SHUT DOWN LEFT ENGINE. ON ATTEMPTED START THE ENGINE WOULD UNFEATHER AND RPM WOULD INCREASE TO 15 PERCENT BUT FUEL FLOW AND IGNITION WERE NOT EVIDENT. LEFT SPEED SWITCH 10 PERCENT FUNCTION FOR IGNITION AND FUEL FLOW WAS SUSPECT. SWITCH REPLACED - NO GO. LEFT, 5 AMP CB REPLACED - NO GO. FURTHER INVESTIGATION FOUND THAT SOME REDUNDANT WIRING WAS SHORTING THE START CIRCUIT. THIS AIRCRAFT HAD BEEN ORIGINALLY CONFIGURED WITH AN OPTIONAL L/H SPEED SWITCH OVERRIDE. THE SWITCH HAD BEEN REMOVED BUT THE WIRING HAD BEEN LEFT IN THE AIRCRAFT. THESE WIRES HAD SHORTED.