The hitch you are referring to is a pick up hitch, the hitch picks the trailer tongue up, they are extremely popular in the UK and are non existent in the USA. Some of these where actuated off of the rear three point of the tractor, when the 3pt was down the hitch was also down. However you could disconnect the hitch and pin it up, perhaps yours needs connected to the rock shaft on the 3 point? Other units used a separate hydraulic cylinder and valve to control the hitch, however this was more common on the larger tractors.