If you are talking of the hayco connector try inserting it from the back side of the backer plate and squeezing it with a pare of channel lock pliers as you push it into the hole. I say channel locks because the jaws can be opened so the jaws are just slightly bigger than then the hayco connector and thus the pliers close the hayco rather than slip off the connector.
This also works for removal squeeze and pull out when removing.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles