Hofline VW Mods

Retrofitting a MK7 Multi Function Steering Wheel in a MK4

This guide will show you how to retrofit a Multi Function Steering Wheel (MFSW) from a MK7 in your MK4 Golf/Bora/Jetta. At this point in time this guide is not yet complete.

Introduction

Working principle

The main issue when trying to fit a MK7 MFSW in a MK4 is the lack of pins on the steering wheel's clock spring and the unknown communication protocol. The MK4 clock spring has 5 pins 4 of which are used for: Airbag input, Airbag Ground, Horn input, Horn ground. This leaves one pin remaining.

To get another free pin we will take the horn ground and connect it to a grounded metal part of the steering wheel and use that as ground. This gives us two pins, one will be used to power the buttons, the other for communication, ground for the buttons will also be taken from a grounded part of the steering wheel.

A micro controller (Arduino nano) will be placed in the dashboard, it will send the status of the dashboard lights through the communication wire and a microcontroller placed on a custom PCB in the steering wheel (Original PCB's will be replaced) will reply with the status of the buttons.

Required parts

Required tools

MK7 wheel preperation

Wiring

To make the wiring harness for in the steering wheel you will need to attach the clockspring plug from the MK4 to the wiring of the MK7 as told in the table below, the colors are only for reference to the images (these also show the pin numbers), some of your wires might have different colors.

You will need to put one additional wire in the MK4 plug from a donor MK4 harness since it normally only has 4 wires and you need 5. To remove a wire from the donor harness pull out the pink/black (Black in my case) retainer, then carefully press the small metal tab on the side of the contact to be able to remove it. To insert the wire in the other plug lift up the retainer and slide it in in the same orientation as you took it out.
MK4 Side MK7 Side Description Image
Pin 1 (Blue) Airbag Green Airbag 1 & 2
Pin 2 (Brown) Airbag Black Airbag 1 & 2
Pin 3 (Brown) Spade terminal Horn Input 1 & 4
Pin 4 (Brown) MFSW Pin 3 MFSW Signal 1 & 3
Pin 5 (Black) MFSW Pin 2 MFSW 12V 1 & 3

Additionally solder pin 1 from the MFSW plug (Brown) and the horn ground (Blue/White) to the springs on the back of the airbag to ground them (Image 5 and 6), the springs will press against a grounded part of the steering wheel when you put the airbag in, to get it soldered properly sand the spring a bit first and solder at a high temperature.

Click on the images to show them in full size.

1
2
3
4
5
6

Assembly

Remove the trim containing the buttons from the steering wheel. I find it easiest to start by prying it up a bit at the bottom and then work my way to the top. Dont bend the trim too much or it will break, also be carefull with the leather next to the buttons, it might be caught on the edge of the trim.

Remove the 6 torx screws marked in the image below and take out the button assemblies. Then remove the remaining 8 screws to open them up, I used a flathead screwdriver for this.

Screws that hold the buttons in place.
Inside of button assemblies.

Take out the original electronics and replace them by the custom ones. The three wires visible in the images below are for development and will not be on your electronics. Do not touch the contact points on the PCBs and the rubber inlay, contamination might make them malfunction.

Don't touch the contact points.
Custom PCBs installed

To be able to connect the new ribbon cable you will need to cut away a small part of the original housing. Make sure that the cable is not in the way when when closing the housing. Carefully fold the ribbon cable between the middle wires and route it to the side as shown below.

Ribbon cable cutout
Ribbon cable exit routing

Reinstall the buttons and route the ribbon cable as shown below. Make sure the ribbon will not get jammed when reinstalling the trim on the steering wheel.

Ribbon cable routing overview

Radio/navigation modification

Choose one of the two methods below to send commands to your radio. If you feel like both methods cannot be applied or you do not know which one to apply please contact me and we can figure something out.

A. IR remote simulation

This can be applied if you radio is prepared for use with an IR remote.
Solder wire to IR remote receiver
Solder wire to something grounded in radio.
Attach the ground wire to the signal ground of the dashboard control module
Attach the IR wire to the IR Simulation output of the dashboard control module

B. Pull buttons to ground

This can be applied if your radio's buttons are connected to ground when pressed.
Figure out which side of your radio's buttons is connected to ground when you press it but not when it is released.
Solder a wire to this side of each button you want to control.
Attach each wire to a desired output of the dashboard control module.

Dashboard wiring

Remove airbag
Remove original steering wheel
Remove steering wheel column trim

Take out ground wire
Put in signal wire
Put in 12V wire
Route to dashboard microcontroller

A. IR remote simulation

Radio/Navigation IR wire + Ground

B. Pull buttons to ground

Radio/Navigation button wires

Installation

Put in steering wheel
Torque bolt to 50Nm (37 lbf·ft for the imperially impaired)
Plug in buttons
Plug in airbag

Configuration

If you have chosen to communicate to your radio by simulating an IR remote you will need to go through the following steps to configure the IR protocol and codes.
Download and install the Arduino IDE
Download and open firmware source-code
Set IR protocol
Assign IR code to each button