'12 Yukon brake lights will not turn off
 

The other day I noticed my brake lights were not working. I found the bulbs were burnt out and the fuse was blown. I replaced everything and found my brake lights will not turn off. The 3rd brake light (LED) is burnt out also. It seems I may have inadvertently pushed power backwards through the system from my trailer connector. I have also replaced the brake light switch and my brake lights are still on. The only way to get them off is to pull the fuse under the dash. I am thinking a circuit board may have melted, but I cannot find where the weakest link in the system is. I also pulled each pigtail connection from each side to identify if they were fused together, but still had a brake light on the opposite side. Anyone know where to look or how to identify the problem? I am a little above my head here.