I suggest you pick up one of these troubleshooting lights that has a clip at one end to establish a ground and pointed end to probe connections. Also download a wiring diagram for the the type of receptacle you have (tow vehicle side) and probe the pins on the receptacle. The pin positions are standardized but the actual wiring colors can vary somewhat. The trailer plug side will be a mirror image of the tow vehicle receptacle.
If the truck receptacle shows ok, the problem is with the trailer plug or further back with the trailer wiring/bulbs. For a factory mounted tow pkg, I would expect the truck to be ok, but a wiring issue in the trailer might have taken out fuses for turns/hazards and/or brakes causing you not get the correct response from the truck. The permanently molded trailer plugs tend to be more reliable than those that can be replaced. The replaceable ones require care when rewiring. Tight quarters for wiring, can break internally and easily short inside and take out tow vehicle fuses.
2016 XD 5.0 Cummins Pro4x Pearl White, Build date 4/2016, Conven & Util + Audio, Bumper Step Assist, Dark Chrome Step Rails (needed someplace to clean my boots before entering!), Front & Rear Splash Guards. 2004 Subaru Forester, 99.5 Powerstroke with mods, previously a 2011 Xterra Pro-4X - (a fine vehicle but was upsized by the XD)