Paddle diagram

Cut the wire coming from the horn contact in steering wheel

Take the one end to the Paddle input on controller,

In steering Wheel connect the horn true a 10KOhm resistor

Connect the UP paddle true a 32KOhm resistor

Connect the DOWN paddle true a 56KOhm resistor

there is also an output to trigger the horn relay. (it says 10K in the Diagram below but it is 1K)

The Power to the horn Relay and the power to the Controller has to be  on the same power source, to make sure it works correct, and power not flows backward from hornrelay to controller, (if power on the relay and not Controller)

Simple diagram width NO horn, Any switch would work all we need is one of the 32K or 56K resistor connectet to Ground to get a shift

Nice W123 steering wheel with paddles from w204 (pics) right colour and cheaper than slk paddles

Thanks to Matt, for sharing this info

Car is w210 manuf. 97

Written by OF Gear ApS / Ole

I have not tested this myself, so use on own risk. 

Written by Matt owner of the W210

The Yellow Wire in the Steering Wheel is Vehicle Ground and transfered to a brown Wire below the steering wheel.

The three Resistors have to be on the Black Wire which is seen in the first Picture.

This black Wire in the Steering wheel transfered to a Yellow Wire after it goes straight throug the steering column.

So you have to cut the yellow wire on the third Picture which is directed to D12 on the Controller and retourn with another wire from D5 of the controller to the Horn Relais.

Click picture to see in BIG format