Assuming I am understanding your question correctly, you need a Class III/IV receiver.
You also need a 7-pin trailer electrical connector (often referred to as a Bargman connector, named for one of the major manufacturers of the connector). This connector is wired to provide the TM with brake and directional lights, running lights, backup lights, a 12-volt battery charge line, and an electric brake line for the brake controller you will install near the steering wheel.
I would expect both of these to be either standard on a vehicle like an E350, or part of a factory-installed towing package. If you already have the tow vehicle, and it lacks the receiver and Bargman connector, then any hitch shop (such as U-Haul, but there are others) can do the job for you.
Hope this helps.
Bill
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