First according to what I can find the hoppy 40165 is a 4 wire trailer hookup not the 7 way blade.

Second, what do you mean the blue wire is a brake light? The blue wire should get voltage whenever the brake pedal is pressed in the truck, that is how the electric brakes work. The actual brake lights for trialer wiring are wired seperate for the left and right sides (red and brown). That is what allows the flashers to work.

Here is a link to a page that shows what wire color is what, and what blade is what.
http://www.rverscorner.com/wiring/7pole.html