DIY steering wheel radio controls

Contributed by:
Keith Burrell

This was a project I undertook so I could control my car stereo using the controls of a Tiptronic steering wheel (I have a six speed transmission). I also used the project as an opportunity to upgrade to the 3-spoke steering wheel. Since my radio has a Sony external wired remote input I could control the radio using a Sony RM-X4S or RM-X2S wired remote. These wired remotes are just resistor networks that give a certain resistance for each radio function. To control my radio, I just needed to add a resistor to the Tiptronic buttons for each radio function I wanted. Currently the steering wheel controls volume up, volume down, next track, and previous track. Although this DIY applies to a Sony radio that accepts an external wired remote input, I believe it can be adapted to other radio applications. I offer some suggestions at the end of the DIY.


Porsche parts required:

Other parts/tools needed:
Step 1:

First disconnect the battery. Remove the steering wheel, airbag, and plastic trim cover.  Undo the screws holding on the airbag using a Torx T30 socket drive. Disconnect the airbag connector and remove the airbag (store the airbag with the padded side facing up). Remove the nut from the steering wheel using a M 24 hex socket. Turn wheel straight-ahead and mark position of steering wheel to steering shaft. Lift off the steering wheel and the spring washer. Undo steering wheel trim cover screws on the front and both sides of the unit. Remove the screws from the steering wheel contact unit but do not remove the unit.

Step 2:

Take your Tiptronic steering wheel and disassemble the Tiptronic steering wheel control buttons. First remove the horn contact ring  (not shown in photo) by unscrewing the torx screws using a T25 bit. Next remove both button covers by unsnapping them from the switch assemblies (be careful not to break the buttons). With the button covers removed, remove the exposed screws on each side of the wheel that hold the switches to the wheel. Now you can remove the Tiptronic switches from the steering wheel.

Step 3:

Add resistors (for a Sony radio) to the switch assembly to control the radio functions. The Tiptronic switches are made up of two different switches wired together to control shifting of the automatic transmission. These two sets of switches allow for up to four radio controls. Using the table below, add the appropriate resistor or resistors after each switch for the functions you desire. Because of the way the buttons contact the switches, make sure that you add the right resistor where you want it.  Review the Tiptronic transmission section of the 993 factory wiring diagram to see an illustration of the switch wiring. Basically one side of the "+" switches are wired together and then tied to one pin and one side of  the "-" switches are wired together and then tied to another pin.  The other side of all the switches are tied to ground. To modify the buttons, add the resistors, connect all the switches to the same pin, and connect the switch ground to the other unused pin (see diagram below). I soldered all the resistors and all the rewiring to ensure a good connection and to save space. However, you could also use splices and crimp connectors to make the modifications. Use electrical tape and/or shrink sleeve to insulate all the connections.

                  Before                                            After

BR/YE= Brown/Yellow wire. BR/RE= Brown/Red Wire, BK= Black wire
Resistors in series 
function ideal resistors actual
Volume Up+ 16690 12K + 4K7 16700
Volume Down- 23610 18K + 5K6 23600
Next Track+ 8656 8K2 + 470 8670
Previous Track- 12000 12K 12000
Front/Back 33545 33K + 560 33560
Middle 48125 47K + 1K2 48200

Resistors in parallel 
function ideal resistors actual
Source 2077 5K6, 3K3 2076
Attenuate 4338 56K, 4K7 4336
Back/Front 6477 18K, 10K 6429

Front, middle, and back are special Sony radio functions.

Step 4:

Check the operation of the switches using a voltmeter to ensure that each switch gives the correct resistance. You don't need the exact value shown in the table but you need to be in the ballpark. Reinstall the switch assembly back into the steering wheel by reserving the previous steps.

Step 5:

Remove the steering wheel contact unit that was left on in step 1. To remove the unit, take off the two screws and unplug the connectors attached to the harness on the unit under the dash. These connectors may be wire tied to another harness so you may have to remove the wire tie before you can get the connectors separated. Install the new support for contact (horn contact) reversing the previous steps. Please note where each connector is located because they are not keyed. You can identify the correct connector locations by the wire colors.

Step 6:

The new support for contact (horn contact) has three connectors - one for the horn, the air bag, and the tiptronic controls. Once the horn and air bag connectors are plugged back in, the tiptronic control connector will be free. At this point, you can plug in the optional Tiptronic Wiring Harness (000 043 203 10) to extend the connector wires, make your own plug in connector, or cut away the connector and splice right into the wires.

Step 7:

Next you need to make your own 3.5mm stereo plug harness for the radio connection. Using some 20, 22, or 24 AWG wire, connect/solder one wire to the Tip ("right"): resistor sense of the 3.5mm stereo plug. Connect/solder the other wire to the ring ("common"): ground of the  3.5mm stereo plug. The "tip" of the plug is usually the "right" wire of the stereo plug and the "ring" is usually the metal sleeve shield of the stereo plug. Insulate the connections with electrical tape.

Step 8:

Now connect/solder the "tip" wire of your 3.5mm stereo plug harness to the wire or pin of the support for contact harness that is tied to the resistors. Connect/solder the "ring" of the 3.5mm stereo plug harness to the wire or pin of the support for contact harness that is tied to ground. Check the operation of the switches again using a voltmeter to ensure that each switch gives the correct resistance when pressed. To check the resistance, connect one lead of the voltmeter to the tip of the 3.5mm stereo plug, connect the other lead to the "ring" of the 3.5mm stereo plug (the ring is the third metal section furthest from the tip) and press each tiptronic button. You may have to adjust the range of the voltmeter to read all the resistances.

Step 9:

Finally connect the 3.5mm stereo plug into the radio, reinstall the plastic trim covers, airbag, and steering wheel, and reconnect the battery. Make sure that you plug the the connector from the steering wheel control into the connector from the support for contact. Check the operation of the radio by testing all the buttons.

Suggestions for other radios:

1. Pacific Accessory Corporation make a unit called the SWI-X. that is an integration device that turns your car's factory radio steering wheel controls into infrared commands compatible with aftermarket radios. You may be able to integrate the tiptronic controls into this device and program it for your car radio.

2. You could try to hard-wire your infrared aftermarket radio remote into the tiptronic controls and then mount your remote insight of the radio.

3. There are probably some other creative solutions that I have not thought about.

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