I got an '07 Titan in May. Has the Big Tow package. Got it to tow a 19' Travel Trailer. I assumed that one of the leads on the 7 round plug would be a charge wire for the TT battery (as in Titan provides charge to TT battery while going down the road). Checked all leads yesterday, and that seems not to be the case. Running lights, trailer brakes all function fine. Should the charge wire not be a standard part of the set up?