The control switches which operate the two front seat head restraints are not functioning. The other controls which operate the various seat movements are ok. I can hear what sounds like a relay clicking under the seat, but no movement. After many times operating the switch the headrest did move up and down a few times, but later was not working again. Can anyone point me in the right direction to solve the problem? The car is a 2003 CLK 320 Coupe.