Three diodes are used for circuit protection. A 1N5408 3A coil suppression (flyback) diode with quick-disconnect terminals came as part of the motor/controller/contactor package. The terminals make it easy to connect to the contactor coil.
A MR752 reverse protection diode is wired upstream of the contactor coil, per the controller wiring diagram.
A 1N4148 flyback diode is wired across the coil of the smaller relay. The bands of the flyback diodes go on the high voltage side.