When I bought my ATC Cougar, I changed from the usual way of wiring a truck for power and lights on a popup. I went to the standard 7 pin plug and receptacle system that hard side campers and fifth wheel trailers use. The reason I chose to do this is because there are plug and play wiring harnesses made for many trucks, and if there is one made for your truck, it makes life much easier, On my my F350, I drilled a hole on the inside of the driver side bed wall, then routed the wiring harness (under the bed) back to the hitch area. Next step is to disconnect the truck harness from the trailer lights connector, insert the tee fitting of the new harness between the existing harness and back of the hitch plug, and reconnect things. That was it for the truck.
When Marty arrived with my Cougar, we connected the camper wiring to a new 7 pin plug. The pin configurations are standard, so it was just connecting the 3 camper wires to the appropriate pins.
To be honest, I don’t understand why this isn’t the standard for all campers. The harnesses are inexpensive, and can be found at eTrailer/Amazon/auto parts stores. If I ever decide to go to a lithium battery, I will simply remove the 12VDC power side of the camper plug, then add the heavier gauge wires and Anderson connectors that are needed for a lithium system.