OK I've poked and prodded with the voltmeter and am now confident that the culprit is the "15 AMP TAILLIGHT CONVERTER AUTO CIRCUIT PROTECTION" module that is located on the inside of the rear interior panel, behind the driver's side taillight. There's voltage going into the converter, and voltage coming out - except for the right signal line. I've searched for the part and can't find it anywhere. The dealers don't sell it separately, but is included in the trailer wiring kit from Toyota for $190!

Any ideas? I'd like to keep it Toyota if possible... Would anyone who has removed their factory hitch be willing to sell me their converter?

Thanks.
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