etrailer.com is the best place to get a wiring kit (and bolt on hitch) for a 2007 es 350.
because the lexus light system doesn't carry lots of current you have to have a kit that runs a heavy positive wire to the battery from the wiring switch box in the trunk or you might blow the computer out.
mine taps in to the existing wires in a traditional manner which seems to work okay (knock on wood).
if you can find a kit that just plugs into your existing harness go for it, it'll be worth the extra bucks.