The headrest monitor in the driver's side seat won't turn on, and I am wondering what might cause this. Is there a fuse that goes to just that monitor? The passenger side monitor is turning on just fine.

 

I had this exact same problem and it just started working again as mysteriously as it stopped. If I think back it may have started working after I had the car in for some sort of service which makes me think maybe just unhooking the battery for a few minutes may 'reset' the gremlins.