Rear defogger not working on 2002 Audi A6 Quattro

When I press the rear defogger button, the red LED lights up if I hold my finger on the button, but as soon as I remove my finger, the light goes off. It seems like the toggle switch is not "sticky" and I can't turn on my defogger. I have checked the fuse box and the defogger fuse is fine (not blown). Any suggestions on how I can troubleshoot the problem is greatly appreciated, thanks!

Asked by for the 2002 Audi A6 Quattro