Abstract: A motorized lift for a trailer dolly that can be retrofitted onto an existing manual trailer dolly lift mechanism without disabling or impairing the manual lift capabilities of the lift mechanism comprises an electrical motor and an integral reduction gear assembly mounted on the leg of a trailer dolly and drivingly connected to an input shaft of the manual gearbox of the manual lift mechanism. An extension shaft on the input shaft makes the input shaft longer so that the manual crank can still be attached to the input shaft for manual operation of the lift. The motor drive assembly includes a manual disengagement button that permits the output shaft of the motor and reduction gear assembly to be disengaged and rendered free wheeling, so the motor drive does not impair manual crank operation.