Steering wheel harness wiring diagram

Hello all,

Building a custom button plate/quick release steering wheel setup and need some help. Can someone provide me with the wiring diagram and layout of the DCT steering wheel harness? Looking to wire the horn and M button and need the wiring diagram if anyone has it. Thank you!

TheGr33k wrote

Hello all,

Building a custom button plate/quick release steering wheel setup and need some help. Can someone provide me with the wiring diagram and layout of the DCT steering wheel harness? Looking to wire the horn and M button and need the wiring diagram if anyone has it. Thank you!

You’ll just add connections via ground for various button requests. You don’t use or tap into steering wheel harness. Here’s KMP documentation for various inputs. Enjoy!

DRLane wrote

You’ll just add connections via ground for various button requests. You don’t use or tap into steering wheel harness. Here’s KMP documentation for various inputs. Enjoy!

DRLane thanks for that! By chance do you have the pin diagram/layout specific to the buttons on the OEM wheel? Trying to find the pinout itself.

TheGr33k wrote

DRLane thanks for that! By chance do you have the pin diagram/layout specific to the buttons on the OEM wheel? Trying to find the pinout itself.

No - I believe most of those buttons are communicating via CAN. There won’t be a way to repurpose.

DRLane wrote

No - I believe most of those buttons are communicating via CAN. There won’t be a way to repurpose.

Even worse, they are an analog signal through the clock spring to the SZL, which then sends the CAN packets on the F-CAN to the JBBF, which passes them to the PT-CAN and K-CAN as necessary. There is no real way to repurpose the buttons.

Thread resurrection…
I’ve retrofit MDM mode to my 09 M3 track car that did not have it from factory by installing a clock spring from an MDM car.

Problem is I have a detachable steering wheel so no button cluster on the wheel to activate it. With a little reverse engineering and too much time with my multimeter, I found that the MDM button on the cluster sends an analog message to the SZL with 82 ohms of resistance. All 4 buttons on each side of the cluster send their analog message through 1 wire, and each button has a different resistance. My assumption is the SZL interprets the different voltage or current it receives from the different button presses to determine whether to activate MDM vs. change the CD vs. alter the stereo volume.

I wired a switch on my wheel with an 82 Ohm resistor in-line. Good news is it works, but frustratingly only about 1/3 to 1/2 of the time. I’ve tried troubleshooting by removing variables like the switch (touching the 2 bare wires together) swapped out the resistor, and bypassing the 11 pin connector in the detachable steering wheel hub. Still inconsistent. Tried numerous combinations of cycling the ignition, turning MDM off before shutting down the car, dirty looks, and screaming loudly. None seemed to make a difference.

I’ve addressed it by adding a 2 pin connector in parallel so I can plug my stock 4 button cluster in to activate MDM, then unplug it and stow it. This works reliably every time when I use the stock buttons. MDM stays on for that session, but next session is another flip of the coin.

My guess is that that there’s more to the stock button than a simple resistor, and that there is something about the “shape” of the analog message that I am unable to resolve with my multimeter, but might be evident on an oscilloscope.

I am not an engineer, and I only pretend to be one in my garage. I’m hoping there’s an EE (or just someone with a better understanding of electronics) who can point out my folly.

Current setup is workable, but it drives me crazy that it works sometimes. I’d probably feel better if it didn’t work at all.

Thanks.