I just had my Styker 2918 toy hauler serviced they had a white cable crimped with a red terminal connected to the POS, which caused me to not have battery power to the lights or jack. I traced this wire and found it to be a NEG grounded to the frame. When I switched it to NEG on the battery, power was restored. Everything works now. Take pictures of everything before you disconnect anything.
So ya they use all colors for whatever trace your wires and use a meter. Saved me couple hundred bucks and the hassle of dropping my rig off.