Depending if your car is left hand drive or right hand drive cruise control wiring will have to be placed on car like this:

Left hand drive:

Right hand drive:

Follow these steps to set up wiring for cruise control:

Car battery must be disconnected prior to any electrical/wiring work done on the car.

Take the plastic part under the steering column off.

Take the light switch out and pull the connector out as well.     

Two wires from retrofit wiring (brown and yellow) have to be routed from cruise control lever place to light switch place (both Left Hand Drive and Right Hand Drive cars).

Remove some cable insulation from light connector so that wires would be easy accessible for splicing.

Splice into wires going into light connector by following:

•    Yellow wire spliced into violet/yellow going into pin 27 of connector

•    Brown wire spliced into black/brown going into pin 31 of connector. There may be 2 brown/black wires in the bunch so double check this if you found the correct one going into connector pin 31

Splicing has to be done like shown in picture

Secure the wires using zip tie 

Put the connector into the back of the lever and push the lever into the guide in the steering column

Route blue wire into engine bay through firewall.

To make this easier we recommend to cut the wire about 15cm form the pin at the end. It will need to be connected/soldered later.

*For right hand drive cars the blue wire has to be routed behind the heater to the glove box side. To do this glove box plastic cover and glove box must be removed.

The wire has to be put through firewall like shown in picture

Following work is carried out in the engine bay.

Blue wire has to be connected differently depending on your Z4 engine. For cars with N46 and N52 (2.5si and 3.0si) engine:

Remove plastic cover using screwdriver with star head. This is what you should see.

You need to get the cable up into this open plastic box. The best way to do this is to use a cable tie and dangle it down in the electronic box, connect the wire to it from inside the car and then pull it up. After this the wire needs to be routed into the IVM.

Open up IVM box by pressing the two switches down on its top. Then pull up the IVM. You should see this.

Get the blue wire next to IVM block. Now you can solder back the pin that you cut before routing this blue wire. Cut the excess of the blue wire (for left hand drive the wire will be a lot too long) before soldering.

Once you have the wire in one piece with the pin open Grey 42 pin block.

Take Grey block, slide out the half of the block (black part of it) and check that the pin 4 in it is free.

Then slide in Blue cable there(Pin 39 in this case looking at the Grey block numbering for double-check) and plug it back in.

Reassemble everything.  

You will also need to cut out a square piece from the bottom plastic panel under the steering column. There is marking which makes it easier to see how much cutting is needed.

Connect the battery. Start the car and test the cruise control.

Do not forget it works only over 60kph and there is no indication about it working on the speedo.