When you are having the problems on your 2013 Scion FR-S do you have anything plugged into the Curt wiring harness # C56212? If nothing is plugged into the 4-Way then it should not be drawing any power from the vehicle tail light connections. The only thing I can think of is if there is a short it could be overdrawing the tail light connections causing the problems you are having. That would indicate a problem inside the converter.
To test the harness, use a circuit tester such as # PTW2993... view full answer...
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