If that solenoid is the same as the Woodwards that Lister/Petter uses... there is an internal switch in the unit that allows it to pull in and stay put without burning up the hold coil. Only two connections are required, but the unit must pull ALL the way in or you will quickly burn it out. On yours the AUX may also be the hold coil, just implemented slightly differently... Look at the Woodward solenoid catalog for specifics of their product. 1502 should be model number. The Chinese copies may or may not conform to the original designs, so your results may vary.
dieselgman