For last three days I have these two warning lights (all the way to the left on instrument cluster) ON. It's '99 ML320, drives as nothing is wrong but lights are bothering me and I would like an advice from any ML owner that had this issue previously solved. I know brake light switch could be the first candidate for replacement. Thanks in advance for help. I'm driving this ML daily for 3 years now and never had this happened to me till now.
Bernard

 

I just had same problem, I replaced the brake light switch and seems to have resolved the problem. I paid 29.00 for switch and it's easy to replace.
Mario

 

Thank you all MBDOC, WOLFGANG, ML 320, Azinn .......for all the advice

I have the 2002 ML 320 Km 136 000
Here is the problem I have not done much: mostly excuses being; 2 small kids and the fact that my ABS ETC etc and eventually the engine light sensor only comes on when it rains, further complicated by the fact that I just rust protected the vehicle underneath and on 2 occasion despite it raining the above sensor lights did not come (I assume the Rust proof agent acted as a waterproof for a while) I did take a visual observation under the vehicle looking for chaffed wires etc but must admit I could have been more thorough - I was shocked to find the one sensor right rear wheel disconnected ???? - remember the Snap-On "obd" reader gives PO 500 "A" indicating left side fault code (and yes MBDOC and Wolfgang said; take it to Merc so they can run a diagnostic on the proper Merc machine and I think he further stressed that they run scanner on the transmission sensor port), however, the ABS, ETS etc. and eventually the engine light sensor are back on again with the rain and will probably stop illuminating the dash when it dries up again.
But now I have an additional/further problem, doing a one direction 560 Km road trip I had no problem Averaging 125 km/h and using speed cruise control but on the return trip on a perfect dry road with he speed cruise control on the cruise control The Electronic traction stabilizer (ETS) started flashing (thereby automatically disengaging cruise control) and on one or two occasion felt a miss/hesitation, but it was not a engine, plug misfire. Under load or acceleration from 100 km/h and up, the ETS - Electronic traction stabilizer would flash intermittently - there where no other lights illuminated on the dash like when it rains, when I pulled into gas station radio off, window open, I felt and heard a intermittent rubbing/grabbing notice and sound from my left front wheel, upon a roadside visual inspection of rotor and pads for obstruction – none find.
My conclusion, Its not a wheel bearing causing the speed soensor to act up as there is no Whining noice eminating from and when I raised the front of the vehicle there was some play on both front wheels at 3 and 9 position, I assume now that there is a front left speed sensor or wiring problem from this point to the fusebox and is sending error code to the computer telling it that I am loosing traction on the front left wheel and braking as a result but I thought the ETS only engages up to 80 Km/h - if so must be real screwed up sensor

Conclusion I hope to do a better visual inspection for chaffing/short and remove Front left wheel and check under fuse box. And thanks to Nisan for you’re good advice OHM meter check on all three sensors remember the right rear one is disconeected - thank you
My reservation to follow MB DOC wolfgang ..... advice yet: is that it has been my suspicion that a wire/electric problem can take many hours and that the Technicians labour book does not specifically say how many hours, perhaps I should tel merc and find out how much it is to run diagnostics (presumably 1hr labour) and what’s the maximum labour that can be charged after that and lights only come on in rain.
So I think I am going to give it one more stab (do I wish I had the WIS or factory manual now !@#$~#$!#$%!) taking the above into consideration and IF I FAIL recognize defeat and call the MERCEDESE MINT Dealership

Thank you all those for their wonderful posts.
I found the problem some time ago - (sorry for the delay) on my ML 320. It happens to be the brake sensor wire chaffed and the wheel speed sensor wires chaffed behind the left rear wheel.
as the wires cross the left main frame and along the gas tank.
The first pic (specifically the corroded area) is the offending section.
Attached Thumbnails

 

Thank you guys for your reply. I came home from work and removed the switch, opened it up to see what is going on with all of them because this is daily repair at the dealer as I heared from mechanic that workes there for 23 years alredy. Some days even 3 MLs with this exact same problem and now I know why. Just another poor design flaw in the simple engineering, broken contact made out of wrong spring steel material that will not last probably even few thousand cycles. No offense, but this switch looks like made in China by Valeo. In the tool & die shop where I work, we make fixtures for testing Boeing and Caterpillar switches and joysticks, cycling them million times back & forth while switching temperatures from freezing to hot within a minute. Quality don't mean nothing for Mercedes any more. I also replaced burned out bulbs in my instrument cluster again, second time in three years / since I own my ML. I never have to remove cluster from my 1980 280SE and they are all working after 29 years of service. I remember replacing two of them, one in the headlight switch and one in heat control ****.
I will make the trip to stealership tomorrow to see what is the latest price for one 001 545 20 09 brake pedal switch or stop lamp switch (as W163 Mercedes Star Manual calls for).

 

Cool pics

When I did my brake switch (this was another repair nothing to do with abs bas est)
a big TELL TALE SIGN was that the cruise control would not engage
I wonder if this is what distinguishes the ISSUE of whether one is dealing with
1) SPEED SENSOR ISSUE OR 2) Brake light switch

I know that when I had chaffed wires - speed sensor issue - The cruise control would engage but would kick out after while

 

Actually, I got lucky as always. Walked into stealer parts department and my body that I know from other Mercedes warehouse for 14 years is behind the counter. I paid just $12 plus $1.03 tax for new 001 545 87 09 revision of original part 001 545 20 09. OEM for less then aftermarket switches listed on E-bay. Nice! Very nice!
No warning lights any more on my instrument panel.
Best regards to all,
Bernard