1) As other have mentioned if you trailer backup lights do they light up?
2) You can use a test light to the blue wire near the solenoid to make sure it is getting juice. Or try and feel it energize when someone puts the vehicle in reverse. (vehicle not running)
3) My 2013 BM quit working shortly after purchase, same thing could not backup without the key. It was the solenoid, the plunger inside is normally closed and is opened up in reverse to allow fluid bypass. After getting the replacement, I took apart the old solenoid and the rubber on the plunger had mushroomed not allowing it to fully open when energized.
Last edited by mcdye; 04-11-2014 at 5:31 AM.