There is not an adapter harness for your 2007 Lexus GS430. To hardwire this controller to your system you can use the Replacement Brake Control Plug-In Harness for Tekonsha and Draw-Tite Brake Controller 12" Long # 20127 to allow you to use the controller between two vehicles with the quick disconnect.
I don't see the wiring needed for your vehicle to use a brake controller, so you will need to do some custom wiring. If you don't have a 4-way flat connection, I recommend the ZCI Circuit... view full answer...