I have a 2015 F-550 w-6.7
The marker lights have always come on when the any of the crew can doors were opened, lightening up all marker lights, but would go out after the door was closed for several seconds. Now they just stay on. I have to disconnect the battery's to put them out. I have replaced the headlight switch, but no help. I even cut all the wires at the bed tail light connection & trailer tow wires, and still they stay on. I have pulled all relays under the hood, and on the pass fuse block, lights still stay on. Even pulled relay behind light switch, no luck. Front markers stay on when wires cut. Any ideas?

 

Welcome on a board.

 

Without a diagram handy, I would suspect some type of problem with the front lighting control module or Body control module. Something is preventing the module from controlling those lights. There is also a good possibility one of the door switches is stuck in the on position. That would be the switches that control the lights as you described earlier. It's a little early for one of those switches to stick since the vehicle is so new, but conditions vary and so do the results. Sometimes a good shot of WD40 into the door locks and linkage helps it disappear.