Do the headphones still work if you swap to an aftermarket head unit? Mine aren't working but I never tried them when I had the stock head unit still in. I've made sure they are set to the right chanel but I still get no sound out of them.

 

Did you run audio to your monitors from your HU? If not then you will have to splice into the harness going to the monitors and hook up the audio.

 

The headphones operate via infrared signals. The emitters are at the base of the screen (you should see some LEDs). If you put a new headunit in, then you have to make sure that there is audio going to the headrest screens otherwise they will not work.