tom,
You will need to call Waymire Group @ 317.634.4824 in Indianapolis to specifically answer your question. They installed the hitch/wiring harness. On the invoice they have listed a wire harness FLT CA and brackect kit. I am sorry about not being more specific since I am not really handy.
I will say, this is my first Lexus and will be my last. My expectations were set to high for this vehicle, and I have had no better treatment with the dealer and the costumer service personnel (800 #) than the Ford dealer down the road. It has all been lip service to this point. Good Luck, Jim