1998 A6 Quattro - Rear window controls do not work

I have a 1998 A6 Quattro and the rear window controls do not work from the 
back seats but the window's do work from the driver's control on the 
driver's door.
Is this a fuse or a wiring issue?  Did not see any fuses dedicated to the 
rear windows

Thanks in advance for any help

Thanks
Bob