I'm at work and can't verify this but I can remember having a similar problem with my trailer when the lights on one side were not working. I went as far as changing bulbs and then discovered that under the hood in the fuse box there are left and right trailer fuses. I found that the left trailer fuse was blown and that was causing the prob. This was on my wife's 2001 Suburban so check it out. After that I started making sure the vehicle was not running when I plugged in the trailer lights because I feel the DTR lights being on caused the fuse to blow because of the arcing.