trailer marker light doesn't work

Don't really understand your post because the taillight and brake light is one fixture with one bulb that has 2 filaments in the bulb on the rear of the RPod one in each lower corner (right and left) the marker lights (are powered when the trailer is hooked up to the tow vehicle and its driving lights are on) are on both sides of the trailer one in the front (amber) and one in the rear (red) and maybe you have 3 red marker lights on the the above the rear window located on the air spoiler.  Also there should be marker lights on each fender.  If you are talking about one of the marker lights on the side of the trailer brake light power does not go to that light.  The running lights power may have become disconnected or the bulb is burnt out to that side light.  You have to investigate it and not sure about the fixture on your trailer but on mine (2019) the light cover just pops off to expose the bulb and that is where I would start.  Hope this helps

Okay. Thanks for the clarification. I don't have the Escape anymore, so I can't compare what I did as I don't remember whether it plugged into the factory 4-way or not.

Again I had the same situation where all the running lights worked and the brake lights as well.  The turn signal didn't.  My tow vehicle warning system indicated turn signal failure and you could hear the flasher was faster.  Occassionally I would see a brake light warning as well.  When I redid the 4 wire plug everything worked so I would check those connections.  When I used to wire trailers my recollection is turn signals were a seperate circuit but brake lights were running light and brake light combined so you got both when you put on brakes.  The OP said brake lights and running were working.

Actually, I mis typed. Both the left brake and the left turn signaling don't work correctly. We checked all the circuits on the TV, plug and cleaned them. They are working well, and then we did get a very weak brake ond turn signal light on the trailer. We think it must be a bad wire (ground?) somewhere along the trailer. We added a bluetooth magnetic light system that we put on the back jacks for a quick temp fixand will have to have it checked by someone with better electronic expertise than we have. But we did have a 3 hour auto zone experience where 2 nice and knowledgeable folks helped us trouble shoot. Our new/used camper needs service. Thank you all for your thoughts.