Center Pin of 7-pin Connector

Gil, I think in an RV application, the center is supposed to be used for backup lights.  Since the T@B does not have backup lights (at least as a stock option), it just sits there doing nothing.  It's kinda like the pin that controls the electric brakes.  Since my T@B does not have electric brakes, that pin is just there doing nothing, but causing no harm.  There are several wiring diagrams for the 7-pin on etrailer's web site that shows the various possible uses for the center pin.  You can check it out here.
https://www.etrailer.com/faq-wiring.aspx