Hi there I recently bought a 2017 Discovery which I plan to use as a tow vehicle for a 1977 Airstream. When I connected the Airstream to the Discovery with the 7 pin wiring harness all of the electronics on the trailer work but the Discovery does not recognize that a trailer has been connected. If I connect a set of magnet lights with the 4 pin plug the Discovery recognizes that a trailer is connected. I am a bit puzzled why the Discovery detects the 4 pin connection but not the 7 pin. I know there is a lot of comments about tow vehicles not detecting led lights because they don't draw enough power but my 1977 trailer has incandescent lights so I don't think that is the problem.

As a temporary solution I have connected both the 7 pin and 4 pin at the same time. The Discovery detects the trailer, signal lights, brake lights, brakes and auxillary line work but for a reason I don't understand the running lights don't. A reasonable solution other than the fact that I would not be able to tow at night.

Anyone have any idea how to resolve my problem?

 

I'm guessing your Airstream has LED lights and your magnet lights are incandescent.

 

Hi Ryan,

My 1977 Airstream has incandescent lights. In the Disco manual it states that the minimum load for Brake/Signal lights is 1.75a / 21W. Not sure if it is possible that the incandescent lights on the trailer are lower than the minimum. I thought that most lights that are not LED would be similar.

 

Yes, 21W is pretty standard for a 12V turn/stop lamp. Might be worth checking the bulb type and your connections.