Repairing Engine Wiring Harness

If the TPE331 engines are the stout heart of your Twin Commander, then the thick bundle of wires that comprise the engine wiring harness must be considered the nerves. And like the heart, the nerves must be given proper care.

The engine wiring harness monitors and controls a wealth of engine parameters and functions including engine and propeller rpm, ITT/EGT, fuel and oil pressures, ignition, NTS test circuitry, and electromechanical-powered fuel shutoff valves, among many other items. The engine wiring harness performs a vital service, and it’s vital that all those wires and connectors perform as intended.

Sometimes a major service involving engine removal, such as hot-section inspection or overhaul, prompts a technician to consider replacing the engine wiring harness. However, that’s not possible. When the aircraft was manufactured, the engine wiring harness was constructed on a layout board, and no part number was generated for the completed bundle. Thus, no new replacement wiring harnesses can be manufactured without creating a new tool—an expensive proposition.

Although no complete replacement wiring harness is available from Twin Commander Aircraft LLC, information on how to repair components in the harness is available. The aircraft maintenance manual has the information needed to perform repairs on the engine wiring harness, including the type of wire required, wire gauge, and connectors.

Some differences exist in maintenance manual engine wire bundle repair descriptions depending on the model. From the 690C on, the repair manual includes a bill of materials for the wiring harness, including connectors. No such bill of materials is in the maintenance manual for earlier models. However, Twin Commander Aircraft can provide a bill of materials from the master wiring diagram. Pairing that information with the aircraft wiring diagram provides the information needed to determine specific repair procedures and materials.

For more information, contact Geoffrey Pence, Twin Commander Aircraft Technical Support at