I've currently got an omp race wheel on my 500 while the normal wheel is off getting covered in black alcantara.
The buttons on the 500 are actually a tiny board with the 4 press switches, one block/button at each side of the wheel. These and the horn connect to a wiring block connector inside the steering column. I can tell you which 2 connections in that block connector are the horn buttons and which are Blue&Me connectors.
The airbag uses 2 wires, a green and a yellow that connect into it, these are separate from the block connector mentioned above.
I took pictures of the wheel in its disassembled state if that would help. I'll have to find the camera cable and get them off the camera.
I've not taken a Panda wheel off before but I'm guessing it would be closer to the traditional horn/airbag combo with the extra buttons added using their own wiring back to the stereo, rather than what I suspect is a canbus module like the 500.