I bought a "Taillight Converter - LED Compatible", NAPA part number 755-2161
Cost was about $30.
This did the job and was easy, just tap into the tail, left, right and brake wires, attach a ground, and you have an output trailer connector with ground - tail - bright left - bright right wires.
The part that I got was packaged with a NAPA label, but it appears to be the same as this part:
Taillight Converter Universal Kit (independent bulb turn signals) :: Hopkins Towing Solutions