Do they come on automatically with the rear window demist or is there a separate control?

Doh..... Just found an old post - there is a switch position for it

 

thanks

Your welcome.

Note they do go off automatically, same as the rear window demist.  The default setting is 10 minutes.  So if you turn them on, they'll turn off after 10 mins and you have to turn off/on again.  As there is no indication of when they're actually on, sometimes you don't know if they're working. 

 

The timeout is adjustable up to 60 mins via VCDS.