THE PROBLEM:
The LED lights on you trailer interfere with your car but works normally when the trailer is hitched behind another vehicle. These symptoms probably mean that the electronics in your car cannot operate LED trailer lights correctly. This is a known problem that occurs in many different shapes and sizes. It may be the case that only some of the lights may work and you are missing, for example, the fog and reversing light. Or maybe they only work for a short period of time and then stop working altogether. Another form of problem may be that the light can be seen to be pulsing or flickering. There are also cases in which the car's on-board computer may try to convince you that you are driving without lights or that some of your lights are not working, even though everything is fine. This is particularly annoying and if you search on internet you will find many complaints but no solutions.
