I have a 2022 RAM 2500 Cummins Larame. I am wondering what gauge wire goes to the back of the truck to the +12 wire (black) in the 7-pin receptacle. If I can pull enough juice through the existing wire to get 10 amps to charge my RV batteries while driving I would be satisfied. I am in stalling a Victron 18 amp DC DC charger in my trailer in order to get adequate voltage to charge my LiFePO batteries.