THE ACFT DEPARTED FT. PIERCE, FL ON A VFR FLIGHT TO KEY WEST, FL, AND DITCHED IN LAKE OKEECHOBEE. WHILE CLIMBING THROUGH5000 FT THE LEFT ENGINE LOST POWER AND STARTED SURGING, THE OIL TEMPERATURE GAUGE FAILED AND SMOKE CAME FROM UNDER THE INSTRUMENT PANEL. THE PLT REDUCED POWER ON THE LEFT ENGINE AND REQUESTED VECTORS TO THE NEAREST ARPT. HE THOUGHT THE ENGINE WAS PRODUCING POWER SO HE DID NOT FEATHER. WHEN HE REALIZED THE ARPT WOULD NOT BE MADE HE SET UP FOR A DITCHING IN THE LAKE. BEFORE TOUCHDOWN, POWER WAS CUT AND BOTH PROPS FEATHERED, BUT THE LEFT PROP DID NOT FEATHER. INSPECTION OF THE LEFT ENGINE AFTER ACFT RECOVERY SHOWED THE OIL TEMPERATURE AND IGNITION WIRES RAN IN A BUNDLE OF 5 WIRES INCORRECTLY ROUTED WITHIN A QUARTER INCH OF THE TURBOCHARGER EXHAUST WHICH BURNED THROUGH ALL WIRES AND GROUNDED OUT THE IGNITION. THE LEFT ENGINE DID NOT FEATHER DUE TO LOW RPM. ONE HR BEFORE THE ACCIDENT, THE NUMBER 1, 4, 5 AND 6 CYLINDERS WERE CHANGED, WHICH REQUIRED REMOVING THE ENG FROM THE ACFT.