I have installed a 5 prong adapter on my Rav4 and all lights work including backup lights. I am upgrading my trailer and putting brakes on it and want to install a Reese IQ 850700 and also plan on using the 3040-P adapter. What I don't understand I see on this forum people talking about a white wire under the dash, but I don't know where it is used in the installation. Also where does the Blue wire connect. If you plug one end of the 3040-P into the Controller and the other end into the Connector under the side panel. How do I get the blue wire to the 7 prong connector?