How to prevent mud/road salt/dirt from entering the rear tail light housing on a 2015 GMC Sierra? This is corroding the wiring harness that the bulb plugs into causing the bulbs to blow.

RTV silicone. I've had to do this on several work vehicles in the past, especially vans with the third brake light mounted over the cargo doors that always seemed to leak water into vehicle. Change the bulbs, apply liberal amounts of dielectric grease, then seal with caulk.

Thanks Ken. My issue is the mud is coming in from the under the wheel well, which is getting flung into the holes attaching its self to the back of the rear tail light. So when I undo the 2 screws from the cabin bed and remove the tail light the entire back is covered in mud. Do you know what I could use to plug the holes to avoid the mud from getting in?