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Outstanding Contributor
971 Posts
Looking good!

I've removed and re-fitted airbag and controls a few times myself, but only assisted once in the removal of the entire wheel.

I believe there's a special type of stitching for leather-covered airbags ... otherwise, yes I'm sure you're right - won't make it through, particularly considering mine is 13 yrs old ...

W220 Moderator
5,624 Posts
Discussion Starter #42
OK, got an hour on the SLK this morning, another C Class Clockspring arrived via Postie, so I whipped the Steering Wheel off, checked the new one was centred, then fitted it, put Steering Wheel back on, and cleared SRS and ABS Codes, then reset Steering Angle Sensor and went for a drive.

SRS and ABS / ESP now stayed off, all hunk dory.

Next up is to finish off the Resistors and then all the Switches will be working, Paddles will be working down to the coiled up 2 Core wires under the Shifter Trim Panel.

Hopefully I'll be at that stage by Sunday night if my customers will stop breaking their Cars :rolleyes:

I have purchased a spare R170 Tiptronic Gear Shifter, so I can do the mods to it, basically solder in 3 wires, and get them exiting nicely into a suitable Wiring Plug, then I can install the modded Shifter into the Car and get Paddles working :devil

Once they're working there will be one last mod to do ...............

The Paddles will work fine, but if you accidentally hit a Paddle when the Car is in P R or N, (anything except Drive D), then the TCU will pop an Implausible Code and the Tiptronic / Paddles will stop working until Ignition off / restart ...................

So that is what the third wire from Shifter is for, we need a small "comparator circuit" to look at the D signal from Shifter, and when it sees that it Switches the Paddles Wires "on" via a 2 pole relay, the circuit I am waiting on details, or maybe even a ready built D-Enable Module from a Paddle Shift guru in USA :)

No biggie, it is quite hard to accidentally hit a paddle, as my Steering Wheel has the, IMHO nicer, "subtle variety" of MB Paddles, rather than the naffing great "Spock Ears" that manufacturers seem to fit these days, just might have to use them with care until the Paddle Guru guy gets time to sort this out with me :grin

W220 Moderator
5,624 Posts
Discussion Starter #43
Well after 2 days locked in the Workshop, phones switched off .........................

Steering Wheel buttons all working 99.9 % faultlessly after a lot of messin', at one point it was all gonna get chucked in the bin :frown

I have Volume + and - , Call Answer / Hang Up, Track /Radio \/ and /\ and then the 2 extreme left "Menu Buttons" are programmed that upper one Switches to Radio, lower one Switches to Media SD Card ................

The 2 "Menu Buttons" are redundant on the R170 as the Dash Cluster does not have all the Menus etc that the "more modern" Benzes like W220 R171 and W203 etc have, so I made good use of them 2 as well :devil

The hassles I had is due to where I put the Resistors in the Switch Plugs, it is very tight when fitted on the Airbag Assy, the wires have to bend at almost 90 degrees as soon as they come out of the Plug, this fractured a couple of Resistors on the first attempt :crying

Second go, both Switches were fine, but somehow, despite me modifying the SWC 1 Pin that came out of the Horn Button Module thingy, it was somehow corrupting the resistances, they worked fine on multimeter but the H/U stubbornly refused to recognise a button press

I ended up wiring both Switches direct to the SWC1 wire from Clockspring and bingo they all programmed in a treat

Steering Wheel is all assembled for the final time now, and it's all working fine :nerd

The only thing left to do is modify the "spare shifter" which arrived yesterday, and then fit that and plug it in to the 2 "Paddle Wires" that are waiting patiently coiled up behind the Shifter that is in the Car :devil

It's not as tidy as I'd have liked with wiring inside the Steering Wheel, but I only see that when I remove the Air Bag, and it's all connected nicely and won't chafe etc, so that'll do for now................

I've proved it works and can be done !!

I have a complete spare Airbag with Buttons, one day, I will build the Mk2 Switch / Horn Button Module set to get it all as neat as I would like .................

The trick, from what I've learned in all this will be to ditch the little MB Circuit Board in Horn Button Module, and run all the Wiring etc inside it's Plastic Casing, and use a smaller custom made PCB for Horn Buttons and Clocksprings Plug in pins !!

Then I'll also use Micro Resistors inside the Switches themselves, and just hard wire to the Pins where the Clockspring Plugs in, which is what I've done with the Paddles :nerd

When one of our youngsters comes up, or when I work out how to do a U Tube Video on my Android Phone, I'll do a Video, but for now you will have to work it out from pictures ...........

The first couple show the (untidy) wiring behind Airbag, but hell it all works, that's the real result :D

I know I can get it tidier though, using the OEM Plugs like I have on the Paddles, (remember this is OEM for a W203 / R171) and not R170 which had none of this malarky :wink

The Brown wire coiled up down by Steering Wheel Bolt is actually SWC 2 to the Android H/U, I'm not using this right now, both Left and Right Switches are wired to White SWC 1 .............

There is a very slight glitch .................

I will probably try the Left Switch on SWC 2 channel as I think 8 buttons on SWC 1 is too much for one channel :nerd

On a very odd occasion, the H/U mixes up the SD Media (lower Menu) button for the "Track / Radio Station Down \/ button", it has happened twice now after many many switch off and re boot fiddle with buttons cycles :wink

Other than that everything works flawlessly. I think just having 4 buttons (Right set) on SWC 1, and 4 Buttons (Left set) on SWC 2 will make that go away ................. 15 minutes at weekend to try that.

The resistances on these 2 Buttons are nowhere near each other in ohms value by the way, I'm certain it is to do with the H/U getting mixed up, it copes fine with just 6 Buttons programmed onto SWC 1 Channel :nerd

Pix :-


W220 Moderator
5,624 Posts
Discussion Starter #45
Hi again :grin


It's my OCD with the way it's done at the moment, it is just not how I'd like it to be and I know I can improve it with a Mk 2 version !!

Ok so it all works, just the one minor glitch that happens sometimes where the 2 Left side Buttons get "confused" as post above states.

The Blue wire has a spade, it is the ground through the Clockspring, which earths the whole metal Airbag Frame containing the Horn Button Module into which the Paddles are plugged as per factory.

Everything inside the Steering Wheel (Horn Relay Buttons, blue arrows in the pic below, Paddles and H/U Buttons) are all NO Switched Grounds, the H/U's Steering Wheel Control Buttons have to all have a different resistance to earth for them to be individually identified by the H/U ...................

Between 25 ohm to 1k ohm seems to be working OK.

I am going to use a minimum of 100 ohm difference in the mk2 set of Parts, as I think the 2 buttons that sometimes get "confused" maybe they are too close after all, one is 180 ohm and one is 150 ohm !!

Yellow is the Horn Relay Wire, which connects through into Horn Button Module and the White SWC 1 is now hard wired to the 2 Whites from the Switches resistor packs, but this should be in between the 2 Paddles "out to Clockspring + & - Cables" in the top 3 pin plug, you can just about see where I chopped it off in the post above :wink

I have now bought a big chunk of "Veroboard", (prototyping PCB board), and I intend to get rid of the larger green Mercedes pcb which has all the redundant CAN stuff on it ...............
My first attempt has proved it is unworkable to re jig it as it's a multi layer jobbie, hence I had to bypass the MB Circuitry and wire direct to Clockspring SWC 1 White wire :frown

I think I will also Wire SWC 2 to the Left Switch Pack, and keep SWC 1 on the Right Switch Pack, I will do this over the weekend to prove (or not) the Switch Confusion theories :nerd

I will make my own simple circuit board to go in the plastic housing, it should be electrically quite a simple circuit, the whole chebang can then run through this when done, and I can rewire the Clockspring to this, as it was intended by MB on the Car models that this Steering Wheel actually came off of :devil

I may try and integrate the 8 resistors inside here as well, but bear in mind, some guys would find this easy, sadly micro electronics is not my forte, I'm just having a go out of necessity :laugh

Pics :-


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