I've had a unusual experiences with trailer light hookups and blinker/turn signal issues. Without the trailer being plugged in, the dash would light up and blink but would not sound audibly as soon as pushing in the brake pedal. I could alway tell when a bulb wasn't flashing by the dash signal flashing fast........it's usually the back bulb. And, sometimes all was needed was remove and reinstalling the same bulb.......there's a connection thing happening. I've recently read that I need to check the screws that attach the fuse box to the fender wells!.........ill try anything at this point.....and don't get me started with passcodes. I've learned there to not let go of the key until the engine has started.