Doesn't sound like a bad box, it sounds like there is a short in the harness, but I'm surprised it isn't feeding back into the system unless the wire to the box is broken between the box and light and the short is feeding the light. Pulling the box would just shut off all power to the truck so a short in the harness would lose power. Take a test light and check fuse 27s socket. With things turned off probe both contacts in the box. You should have power on only one side with the park lights on. If you have power to both there is a power short in the circuit outside the box. It would be a mess, but you could try pulling other fuses. Turn the lights on park and be sure they are all on, now turn them off and see if the right front is still on. Take a test light and connect it to ground, then run down the fuses in the box, find the ones that have power on both sides and pull them one at a time and see which one turns the light off. That would at least point to the circuit that is feeding it power.
Being you know how to pull the box you could try a test, pull the box, now use a fused jumper lead connected to the battery positive and go to the output from fuse 27 that is in gray connector X1 under the fuse block. Use the jumper to feed pin F5, that is the right front power feed to that light. Does it come on? What else comes on with it? Pull the light assembly out and check the connector for any issues. The brown wire is the marker feed.
Pull the connector up out of the fuse box connector assy, see any rubbed wires or corrosion there?
Worst case you could trace the harness across under the radiator and look for damage or corrosion. I'm betting that the turn and stuck on lights are because of something in the harness but finding it could take a bit.
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Wednesday, February 2nd, 2022 AT 9:37 PM