Mk1 horn help please

Hi when I finished my caddy I realised I had no horn,
I've found the wire from the head lights black and yellow and that is live when I put the he ignition on, I've had a look at the steering wheel and the plate on steering wheel is not live or anything how does it all link together ? 
All my other lights and everything else is working so I'm a bit confused, I've purchased twin horns and they are ready just wondered how it all linked to the steering wheel and why is the wire in the engine bay always live when the ignition is on and not linked to button on the steering wheel if that makes sense 
Thanks guys 

Lots of horn problems lately ,:lol: see my reply from a recent thread;

When looking at the horn remember VW wired them differently from the rest of the automotive world. Most are earthed to the chassis where they are fixed and pushing the horn connects +ve 12v.

With VWs of this age they are feed with +12v when ignition on and pushing the horn on the wheel connects to earth.

Sometimes there is a bad connection at the steering wheel, there is also a earth wire that connects the steering column/rack to the bulkhead. Unfortunately this located is in the engine bay quite low down and gets corroded and drops off.

If twin horns (and single?) there is a relay in the circuit too. As the wiring ages and resistance builds up not enough power gets to the horns to make them sound. A quick fix is to disconnect one horn leaving enough juice to power the single remaining horn.
 

Thanks for reply, so if I earth the column and attach the horn to yellow and black wire which I found earlier should make the wheel live when horn is pushed? And complete the circuit? As the yellow and black wire is always live when ignition is on ? 
Thanks again 

The Steering wheel is Grounded at the Frame of the Steering rack mount, to the Steering gear Box.

From there it travels up to the (turn Signal switch Wiper finger) to meet with  the back side of the steering wheel)…..

here is a simplified diagram.