Got a weird problem with my left hand side number plate light, it comes on when I unlock the car then goes off and 10 seconds later comes back on again I metered the wire and it shows just under 15v and then it drops to near enough 0v. Has anyone else had this problem? It's doing my nut in and I'm hoping it's nothing major
w203 rear number plate light strobing
brucemillar
MB Enthusiast
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15v seems high. You need 12vdc. Is your meter good?
Has somebody fitted leds? they can strobe if not the correct type? try swapping bulbs or look for damage in the loom where it joins the boot lid.
Has somebody fitted leds? they can strobe if not the correct type? try swapping bulbs or look for damage in the loom where it joins the boot lid.
I originally thought it would be cause I fitted leds but it's the same on normal bulbs aswell the other side is completely fine I'll get my other meter and check the wires again tomorrow and check what reading I get
grumpyoldgit
MB Enthusiast
Are you saying that it's set to come on with the other courtesy/side lights when you unlock the car in the dark and the other lights stay on, or is it coming on on it's own without the other lights day and night?
The rear SAM will turn off a bulb that it thinks is failing - so I suspect the SAM has decided there is a bulb issue and turned the power off.
I presume you have tried a new bulb (from MB dealer, not Halfords)
The only thing that concerns me with my own thoughts above is that I thought both bulbs were wired together - but it could be they have individual connections to the SAM
Richard
I presume you have tried a new bulb (from MB dealer, not Halfords)
The only thing that concerns me with my own thoughts above is that I thought both bulbs were wired together - but it could be they have individual connections to the SAM
Richard
SavMan
Authorised Forum Sponsor
Disable the convenience lighting feature I found that if the car did not see the error after several start's it could then be reset with standard bulbs.
I ordered some replacement LED's and ran good quality standard bulbs until they arrived. I then ran the LED's without convenience feature for a couple of days before re enabling. This set has been OK for about 4 months now.
I ordered some replacement LED's and ran good quality standard bulbs until they arrived. I then ran the LED's without convenience feature for a couple of days before re enabling. This set has been OK for about 4 months now.
I originally thought it was the bulb too but I swapped the bulbs from left to right and it worked perfectly on the right side.
Sorry for the noob question how do I switch this off? Is it done from the menu or do I simply flick the light switch to disable auto lights?
grumpyoldgit
MB Enthusiast
Convenience lighting is turned on/off in the menu. Remember there are options for them to operate on both lock and unlock, so you may need to turn both off. Details are in the User Manual. (If you don't have one ...... shout and I'll try and find the link to the online ones.
Diagram of sidelight circuits. Separate connections for L & R hand lights.
Diagram of sidelight circuits. Separate connections for L & R hand lights.
grumpyoldgit
MB Enthusiast
I'm not sure about that, but Richard from Comand Online (post #6 above) would probably be able to answer that for you.
I think if it were me that I would try SavMan's suggestion, (post #7 above) with new MB bulbs fitted and see how it goes.
Do you have a User Manual to check on how to disable the convenience lights?
I think if it were me that I would try SavMan's suggestion, (post #7 above) with new MB bulbs fitted and see how it goes.
Do you have a User Manual to check on how to disable the convenience lights?
riz_k - assuming above diagram is correct, it is then either
SAM
Wiring / holder
Lamp
I would put back a standard bulb (not LED) in that holder having cleaned all the holder contacts (bulb and where the connections plug into it) and see if it still occurs. If no longer, then its probably the SAM and the LED bulb being not quite compatible, - i.e SAM detects a bulb fault and turns off the power - possibly something in the bulb heating up and resistance changing ever so slightly..
Richard
SAM
Wiring / holder
Lamp
I would put back a standard bulb (not LED) in that holder having cleaned all the holder contacts (bulb and where the connections plug into it) and see if it still occurs. If no longer, then its probably the SAM and the LED bulb being not quite compatible, - i.e SAM detects a bulb fault and turns off the power - possibly something in the bulb heating up and resistance changing ever so slightly..
Richard
grumpyoldgit
MB Enthusiast
Diagram is taken from a workshop manual which covers all W203 C Class models Sept 2000 through to May 2007. Sorry, forgot to add that info in previous post. 
After turning the lights off that come on when I unlock the car the problem still exists, however when I operate the light switch manually the light functions fine but once I put it back to auto it starts flashing again. Any ideas?
