LOL Gerritt.. it's Sunday and you're in your laneway. Tell the truth buddy....
If it works on the F-in-laws.. your brown wire is off somewhere. Tail lights are on...harness should be live.. but you are correct, could very well be a fuse blown if it's a factory direct wired harness.
Flat 5 wire harness is what I have on mine... actually I have a 7 on the truck.. but 5 on the trailer. 5th wire is for back up lights/reverse lock out solenoid on the surge tongue...so you can back up and not have the brakes come on. Round 5 wire plug used for brake wire on electric brake trailers.