2011 peterbilt 387 lighting problems

You probably already looked for this, but just in case...
The wiring harness for the headlights and marker lights run together and up into the headlight housings. These get a lot of stress on them as they run over the pivot point for the hood opening and closing. I had a shorted out marker light wire to the headlight wires on the driver's side there, and it took out all of my marker/clearance lights. Started eating fuses and bulbs, then I found the short. I know there were a lot of changes on the 387 between 09 and 11, so yours might be different than mine in these regards.

 

If you have a relay box or fuse box by the passenger side tool box. . Check the main wire that's on the top of the panel. It starts to get loose and with the truck vibration. .. it makes everything to do what you just mention. .. when you remove that cable do it with all lights on.. so that you can see what it does and when... then reposition the cable.