Rearscreen not demisting

I have a 1999 MK2. When I bought it, the rearscreen demister loom was missing. I got another one and installed it. The demister came on after I started the car and went for a drive. After that time, it never came on again. I am not sure of I have managed to turn it off, or a fuse has blown, or what to be honest.

Are they “always on”? or is there a switch that I have pressed? My car is the base model, so there aren’t too many switches to have turned off!

I checked the fuses under the bonet, but have not turned up anything blown yet. I think there are also some fuses under the steering column, but it needs closer inspection.

Any and all ideas welcomed!

Thanks,

James.