May be on the turn signal stalk, or should be located on the side of the dashboard to the right of the steering column.

probably the same place as the front window wiper switch

I've a mk3, think yours might be a mk2, but mine's on the wiper switch, but you have to push the wiper switch away from you, in the same way as you pull it towrad you if you wanted to clean the front windscreen.

Hope this helps.

its on the right hand wash wipe stalk , push it away from you to turn it on push it away again 2 stop it wipping , push and hold away 4 your rear washer ok/ jk