Steering Wheel Wiring

[Foss]

I want to add some extra custom controls to my steering wheel. Does anybody who's familiar with the Sportivo wheel know if there's any unused wiring there (perhaps for other models that have bluetooth/aircon controls) that I could use? I assume it'd be impossible to run new wires to the wheel without modifying/replacing the clockspring or making up some sort of slipring contact? Hence the want to utilise existing spare wiring if available.

[DJKOR]

The steering wheel controls share a common bus and work by varying the resistance. If you want to utilise the existing components there, you will need to have your axillary device tap into the existing controls and then read the resistance values from there. It's not as simple as just opening an closing a switch if you get what I mean.

This should give you an idea of how it all works. The wiring is there on both sides (EAU, AU1, and AU2), the only thing that is missing on those that don't have the on/off hook button etc are the buttons and the appropriate resistors:

[Foss]

I was worried you'd say that. Is there anything unused in there I could connect up to or am I going to have to sacrifice some of my audio controls?

Edit: Scratch that, overlooked that last sentence and the image didn't render the first time.

Edited July 13, 2010 by Paradigm

[Foss]

Right... so...

If I were to get 2 momentary buttons and insert the appropriate resistors into the line after it, then I would just need to reroute the wires behind the headunit to a circuit that can measure the resistance on those wires, whice then triggers a specific action when it detects the appropriate resistance? What if this action was to momentarily close a circuit (eg. pushing the power button of a computer)?

Or am I way off base here?

[DJKOR]

Right... so...

If I were to get 2 momentary buttons and insert the appropriate resistors into the line after it, then I would just need to reroute the wires behind the headunit to a circuit that can measure the resistance on those wires, whice then triggers a specific action when it detects the appropriate resistance? What if this action was to momentarily close a circuit (eg. pushing the power button of a computer)?

Or am I way off base here?

Yes, that's pretty much how you would do it. You would either have the control circuit in series with the steering wheel controls or you can have it parallel with it. If you have it in series, you would need to ensure that the circuit is of really low resistance so that it does not interfere with the existing controls, or if it is in parallel, the resistance needs to be really high. In terms of simplicity, having a circuit in series would be the better option as it would make it just that little bit easier to integrate. As to what circuit you would make, I can't really help you there at this point in time.

[Foss]

Out of interest, what would happen if I just connected a button to the existing wiring without a resistor?

[450HP/tonne]

I want to add some extra custom controls to my steering wheel. Does anybody who's familiar with the Sportivo wheel know if there's any unused wiring there (perhaps for other models that have bluetooth/aircon controls) that I could use? I assume it'd be impossible to run new wires to the wheel without modifying/replacing the clockspring or making up some sort of slipring contact? Hence the want to utilise existing spare wiring if available.

You can add up to 4 wires to the spiral cable, the ones marked "o" are not used by anything on any model globally, but the ones marked "X" have some usage (even if in an overseas market that uses A/C control via steering wheel ... how lazy!).

Source 1: I pulled apart the spiral cable and took the below photo (from a 2009 AT-X):

Note: The "X" on the bottom row is for the display button that would be on the higher grades, like Sportivo. The phone on/off hook uses the existing audio wires.

Source 2: The REAL Toyota repair manual (not the one floating around the net).