Update on the work truck…. I finally decided to get serious on this trailer light issue. Just picked up an ALUMA trailer and I want those pretty LED’s to light up!
After tearing out the Brake Controller and disconnecting all the wires I could trace down (up under the dash)… I still had the problem of truck tail lights staying on once I hit the brakes… or turned on the flashers. I rigged up a couple of spare trailer lights, plugged them in and everything worked perfect. That’s when I decided to connect the ground wires. Yep… same problem! So the ground wire coming thru the harness (white wire) was no really a ground wire. I don’t know what it is for? Don’t really care. I just grounded my trailer light harness into the frame and everything works as it should! Thanks for all the suggestions!
Attached is a photo of my test set-up

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Haven’t had a chance to check for that fuse yet… not sure when I’ll get to it, or if there even is one? Probably my feeble mind playing tricks on me. Might have even been something on my previous truck? Thought about ordering a couple of Diodes to eliminate any backfeed.

I disconnected the auxiliary brake control. They also had a hot wire running back to the plug, along with the blue wire for brakes. Hooked up my trailer and checked turn signals, hazards. All good.
When I tried the brakes, they stayed on. Found out that if I turned on either turn signal, then the brake light on that side would go off.
I figured that might be a way to get me by for a couple short trips, hauling the mower down to the farm. I could just bump the turn signals or the hazards each time after using the brakes. So, I’m cycling through this scenario when I turned on the hazards and they didn’t flash. I go back and the truck taillights are stuck on again but this time, no trailer lights. Only way to get the truck taillights off is to unhook the trailer plug… and there is a blown fuse now for the trailer lights. (I remember that from a session a couple years ago)
Ran out of time and patience!