This is should be an easy modification so you dont really need a wiring diagram. All you have to do is find a wire near the steering column that gets 12v only when the headlights/parking lights come on. Tap into it then run a wire to the harness of the footwell lights.
Its pretty simple.
The following is for the 09-10 tsx but should be the same for the 11/12. Just make sure you test with a multimeter.
This info from Bulldog Security
TSX 2009 -2010
PARKING LIGHTS ( - ) GRAY (-) @ HEADLIGHT SWITCH, (BLACK/WHITE, 12-Pin Plug) Pin 11
PARKING LIGHTS ( + ) RED (+) Left Front and Rear) @ DRIVERS FUSE BOX, (LT. GREEN, 16-Pin Plug) Pin 11