Rear turn signals dont work

Thanks. I have a ground wire attached to the hitch (was free hanging and worked). The end of the wire, with the connector was not round like it should be. Is that potentially part of the problem. Hard to get under the truck to closely check wires. Snow still covers the parking lots. I did try to check my 7 and 4 pins. I didnt immediately see anything unusual. I have a 3rd connection in my truck bed for 5th wheels. Perhaps checking those wires could be in order as well.