There are modules included in the factory tow option that aren't there without. Thats whats needed.I'll have to look into that. There's so many duplicate threads it's hard to read them all. I would assume that there's a switch by the brake pedal that you would tap into for that universal wire signal.... Unless they've gotten so advanced now that they just read off the pressure of the master cylinder and don't even need a switch on the pedal anymore.