A very useful tool that you will have for all your RV needs is to purchase a male and female seven pin connector set and wire each end with one foot long pigtails of the right color. If you can't find the right color wires, put numbers and purpose onto masking tape and get as many right colors as you can.
Then, you can put the correct one into your truck and use a meter to determine what wires work, or you can feed power into the RV from a jumper cable that connects to the correct one for your RV, and see what works in the RV.
It's something that you will be able to use for all your RV uses throughout your life and really cuts down the process of trying to hold meter leads onto screws because you use electrical jumpers with alligator clips to connect your meter to the wires.