They should be the same.
Sometimes the "white" ground wire/pin is not used, and the return path is through the trailer frame, and vehicle ball hitch, vehicle receiver, to vehicle frame, instead of this wire/pin. If ground pin is used on the trailer, typically the associated white wire will only be run a short distance from the connector and land on a bolt or be screwed into the trailer's frame.
So, if it's not used, and the trailer's frame/ball hitch is being used for the path, make sure the vehicle's ball hitch mount (male) has good contact with the vehicle's receiver (female) and paint, rust, or warning labels don't prevent good metal to metal contact that is needed for the return "ground" (-) path.