R129 SL - ADS switch not illuminating.

[Hartzpartz]

.....actually, looking at your wiring diagram (Thanks to Stats007) it appears that all the switch does is provide an earth signal for the ADS ECU. I assume in this case, the switch has an earth wire going to a "console earth" mentioned on the diagram. A bad earth may explain why the LED/illumination flickers when the ignition is turned off (feedback through another circuit in the ADS ECU?).

Has anyone seen this earth wire or earthing point behind the console? Would be handy to know if the switch earths behind the panel before I take it all apart!

Would be excellent if anyone knows where connector "X33/9" is located also as this may be causing the problem.

 

[stats007]

The console isn't hard to take apart - it earths directly behind it from memory - you should be able to see all of this if you remove the radio and air con unit.

 

[Hartzpartz]

Thanks for that stats007. I'll have look when I get the chance and let you know what I find.

 

[Hartzpartz]

Well that wasn't too bad to take apart. Air con controls a little tight to get out but apart from that, quite simple really.

You can actually see all the console earthing points just by taking the cubby hole lining out (1 screw at the front). Alas, none of these were loose.

There seemed to be 5 pins on the ADS switch, 3 x 12 volt pos (one live only with light switch on), one earth (brown) wire and one open circuit wire (I assume this goes to the ADS ECU).

I was hoping the brown earth wire would be open cicuit but it has continuity to the console earthing point.

Do you have a more specific wiring diagram (stats007) showing the configuation for all the wires?

It appears someone has been tinkering in this area before as the radio has a few crimp connectors and the wiring is a bit messy. It still has the original Heidelberg RCM 40 radio. Maybe this was a dealer fit option and they weren't very competent at fitting radios??

 

[stats007]

This should help:

 

[Hartzpartz]

As a post script to this thread, when I eventually got round to further troubleshooting the fault with my ADS sport/comfort switch, it turns out the wrong switch was fitted by the dealer when the system was overhauled two years ago. You would've thought they might have checked to see if it worked, especially as the bill (for the previous owner) came to over £5400!

The switch fitted (129 820 99 10) has the same 5 pin configuration but different internals. Thanks to Merc quality I was able to open the wiring plug and easily swop the female "pins" around to make it work.

Switch now illuminates, LED lights with key in position II and it switches to sport mode when the switch is pressed and the engine is running! The correct switch number is 129 820 96 10

It's very unlikely that anyone else will have this problem but who knows?

Thanks again to Stats007 for his help with wiring diagrams etc.

 

[television]

Stats has more 129 info than MB