Before coupling a converter dolly to the rear of the first trailer, you should:

Coupling a converter dolly requires alignment of the dolly's tongue (draw bar) into the pintle hook on the rear of the lead trailer. The driver must visually align — sometimes with a spotter — to bring the tongue eye directly into the open pintle hook, lower the dolly's landing gear to the appropriate height, latch the pintle hook closed, secure the safety chain or hook latch, and verify the lock is fully engaged. The dolly's parking brake (if equipped) should be set during the coupling process. A misaligned coupling can cause the connection to fail under load, dropping the dolly and second trailer on the road.