Warning about brake controller testing: A METER may not offer enough resistance for the controller to "see" a load (imitating a trailer plugged in) and allow voltage to be sent to the Blue Wire. The cheapest test light (little ice-pick-looking thing with a lamp inside and a wire and clamp on the other end) you can find WILL offer that resistance. Apply the brake controller manually and the light should glow and brighten as you squeeze.
I've used and worked with and on these things but not a whole lot. For that reason I don't know if the controller should send voltage from a brake pedal press if the activation method is "inertial" (pendulum in the controller responding to slowing motion of the truck as in braking).
In addition to polishing the contacts, I'd try getting to the connection sides of the truck socket and trailer plug. See if anything's loose. See if you can trace the trailer's 7-pin cable to a junction box and check there. Connections to the brakes at the axle of course. This is a new trailer and something could have not been properly connected/tightened.
