Originally Posted by Tom N3EQF
Before we go trying to prove or disprove what we read on the Internet ("...it must be true then"), I am of the belief that if the auto manufacturer spells out a step-by-step procedure for towing the vehicle they designed, I am going to follow their procedure.
In the case of my vehicle, I can see that the transmission is electronically controlled as the dash display tells me if the transmission is "ready". It seems to me that leaving power on the vehicle in any fashion leaves open the possibility of that transmission doing something different than "Neutral" while towing.
Adding an Auto or Manual switch on a main battery lead will satisfy the requirement for little expense compared to the whole towing package. If your aux braking system requires power, that's easy to wire directly to the battery and/or a charging line from the RV.
I don't disagree with following the directions. The reason my system was done this way was because the installers (a very reputable hitch installation dealer) assured me that this was the way. The aftermarket installers located in my local Ford dealer also told me that when they do towbar installs, they do the exact same thing. I probably should have just put my foot down and insisted that they put the other pieces on (the battery switch and the extra direct-wired 12V plug) but we're beyond that point.
As for my specific vehicle, the power is not left on in the vehicle. You start the car, you place the vehicle in neutral, and you turn the car off. There is nothing electrical running at all: no radio, no HVAC, nothing.
As for your last statement, running your power to the aux braking MUST be done from the vehicle, never from the RV. If you were to have a breakaway, the car will be a runaway. There will be no power to apply the car's brakes.
What I will probably have to do (as we are leaving on Friday) is manually disconnect the battery cable and buy one of those inexpensive 12V jump starters. I can leave it in the cab of the car to power the aux braking system and give me piece of mind that things are ok.
Thanks for your input!