Abstract: A safety interlock mechanism requires a trailer tow bar to be raised and placed into the mechanism before an electrical power supply cable can be removed from the mechanism and attached to an aircraft. Similarly, the electrical cable must be disconnected from the aircraft and placed into the interlock mechanism before the tow bar can be removed and placed onto a tractor for movement of the ground power unit. The safety interlock mechanism includes a hinged plate, which, in one position, prevents the removal of the electrical cable connector when the tow bar is not in place, and when in another position, prevents the removal of the tow bar when the electrical cable connector has been removed. Locking tabs engage the electrical connector whenever the tow bar has been removed. A locking pin engages a U-bolt attached to the tow bar whenever the electrical connector has been removed.