I have to agree with donn0128, fix it or replace it. No one has suggested fixing it, so I will. Take the vehicle socket(male)and disconnect it from the vehicle and the cable, then take the cable plug(female) and disconnect it from the trailer. Now sit down at your work bench or any well lit place and plug the two parts together and try and observe where the problem is. Often it is a lousy casting or a socket or maybe a foreign object in one of the sockets in the trailer plug. There is something wrong with one of the two mating parts. If your truck came with the seven wire connector and the trailer with another brand, could be they weren't meant to mate.
And yes in my 60 years working mostly in the electrical field, I have run across this problem more than once where there is no "Written Standard" like the NEC. Even in the four wire flat connectors, there is a huge difference in plug ends.
I'd take both ends to NAPA or U-Haul or some company that has several makes of connectors and try and mate up one of the connectors to a new one. It may require spending some of your hard earned money but those bungies cords or what ever it is you jerry rig your connection weren't free.
By the way we're talking about less than twenty dollars and in most cases less than ten.