Pulling my 2021521L and my truck (Tundra) won't recognize I'm towing anything. All of the trailer lights/signals work however the brakes do not engage when braking. Had the same issue pulling an airstream several months back, would let me set gain on towing mode but the braking was intermittent at best, most of the time it would just say "no trailer" in the dash. Anyone know what could be wrong with the truck?