If your truck is newer than '95 and you have the green lightcord and only 1 plug on the back of the cab then the "auxiliary wire " is continuously powered for a trailer that is abs equipped
In that case the easiest way is to install a second (usually 4 connector) plug on the trailer and run a second cord to it. If you use a second connector as a ground you can have 2 extra connections (maybe a set of led backup lights)
yes and no chance of mixing them up in the dark
they also make a 6 pin that is about 1/2 the diameter of the 7 pin.
there are choices in the heavy truck parts market without looking at the RV market
and the extra connections can be used for OD lights and rear flashers