Do you have surge brakes on your trailer? If so the back up lights activate a solenoid that disable the brakes so you can back up the trailer. If you don't have brakes or your not going to back up much than you should be OK. If you do back up and incline or on some soft ground that may be enough resistance to apply the surge brakes. So if you find you can't back up that is why. some trailer may have a manual shut off valve too to allow backing up.