I would start by testing the trailer wiring harness, # 118652, you just installed on your 2017 Lexus NX200t. Use a circuit tester like # 3808 and test each function. If the problem is on the vehicle then check for any fuses related to trailer brake lights. If it's not a fuse you'll need to check the wiring connections you made when installing the harness.
If everything checks out at the 4-way trailer connector then the problem is on the trailer. Inspect the trailer's 4-way and make... view full answer...
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