Scirocco Register

Giving the mk1 a pre-MoT check and the horn isn't working. Any tips on likely culprits, or will I have to try to be systematic and check everything?

I'm hopeful it's as simple as T25s, when it's almost always the earth cable at the bottom of the steering column.

Had the same problem on my Mk2.
It was the push connectors on the horns themselves.
Whilst I was about it, I moved the horns from behind the front valance into the front of the engine bay, loads of room on the driver's side. Next time they need maintenance, I don't have to lie on the floor!

In my experience it is usually the connections at the horn itself.
Disconnect them, check for corrosion and replace the terminals if necessary.
Check you are getting 12 volts at the terminals. If you are, connect a battery briefly, directly to the horn itself.
When you press the horn button can you hear the relay click?