One of the features of a position event object is the ability to optionally add either a TractorReferenceNumber, a TrailerReferenceNumber, or both.

Parameter	Type	Description
TractorReferenceNumber	String	The reference number of the tractor assigned to the shipment.
TrailerReferenceNumber	String	The reference number of the trailer assigned to the shipment.

Here is an example JSON Object:

Completed Advanced PositionEvent Object:

Here is an example of a completely valid basic PositionEvent JSON Object with a Trailer and Tractor Reference Number:

{
  "FreightProviderReferenceNumber":"12345670",
  "FreightHaulerProviderXID":"ABD3820AI",
  "CarrierMC":"3829182",
  "Latitude":50.1234,
  "Longitude":-45.1234,
  "TractorReferenceNumber" : "9302812",
  "TrailerReferenceNumber" : "1654895",
  "PositionEventType":3,
  "PositionReportTime": "2017-03-20T17:52:22"
}