relay is in slot 2, the fusebox is under the dash, passenger side. note your car is still a MK1, not a MK2

cabby was based on MK1 shell right the way thru production till the MK3 cabby came out, just with a few facelifts to make it look a bit more modern.
have a look at the fusebox faq, the fusebox relay locations are on page 2, you want to be lookign at the pictures for pre-90 MK2 Golf. Also, scroll down a bit more and there is a list of relay numbers and what they do.
http://www.golfgtiforum.co.uk/index.php?topic=44637.0