You have to buy a separate junction box if the RX did not have a tow package. The directions with the box will tell you where to plug it in. There is also a fuse in the fuse box that may need to be purchased and installed to get electric to the hitch.
Where did you plug in the hitch under the cargo area? There shouldn't be a connector that fits the one that comes on the hitch. Also, the hitch cannot be just spliced into the car's electric because of voltage differences. You will not get 12V at the hitch with a splice.
Check this post for the part number of the converter (junction box assembly). The part number may vary by year but it is a start.
http://us.lexusownersclub.com/forums/index...ic=39543&hl
Thanks for the replies. I have the junction block assembly on order from Lexus of Roseville, California. They told me that no directions come with the part, but they think it goes under one of the rear seats. I plugged the connector from the OEM tow hitch wiring into the receptical located above the floor grommet in the rear cargo area (driver's side). There is a 30 amp fuse (#15) in the engine compartment for the tow hitch circuit. It was already installed and checked out OK. I guess without the junction block, there is no power available at the connector. I just hope I can find the old one & replace it with the new one without taking anything else apart.