Rear indicator failure

[Keefmilbo]

Hi,i have a 2012 c220 estate.it has come up with rear indicator left not working on dash and the brake light is now acting as an indicator. I have looked and its a sealed unit with leds. I removed the light unit and put a live and earth to the light unit and the leds all light up fine but when connected to car they sometimes flash once then show fault. Mercedes says i need complete new light at £170. Im going to investigate why they work off car but show fault when connected , i thought at least one led would have maybe stopped working but was wondering if anybody has had this problem and found a remedy. I wil, post if i find solution thanks.

 

[Ken_R]

Almost certainly an Earth fault of some description. Trace the Earth wire (normally brown) back to where it connects with the body. There most likely will be a 'poor' connection. Usually corrosion but, on that year, possibly loose. If you have a multimeter, check the Ohms between the the Earth at/from the lamp unit, to a known working Earth point/clean body fixing/battery -ve.

It should be zero.

If I can't actually find access to a wiring terminal, then I will use a dressmakers pin into/through the insulation of the cable to be tested and connect a multimeter there.

 

[Keefmilbo]

Thank you, I added an earth and it worked for a bit longer then stopped. Now I will concentrate on that. Thanks for the reply

 

[bembo449]

you may also find the circuit board has burned out , saw a merc that had done this last year

 

[Keefmilbo]

Is that inside the light unit

 

[bembo449]

yes , remove the unit and then disassemble so you can inspect the internals , you need to be sure the board isn't fried pal

 

[Keefmilbo]

I did try taking screws out but it wouldn't come apart, I assumed it was glued to lens

 

[Keefmilbo]

All wires perfect added two earth's to be sure checked ohms all good. Put the light that is not working onto other side and still don't work. Put light that works onto side that doesn't expecting it to work and it doesn't. That would mean the light unit and the wiring is suspect. It's only the indicator that is intermittent.
Not sure what to try next, need a light unit to try but can't get one before I buy a new one

 

[Ken_R]

Let me get this right. The fault/problem was on the rear left. You transposed the left (faulty) unit to the socket for the right unit, and still get a fault.

The right (working) unit was transposed to the left socket (expecting it to work correctly) and it doesn't. It displays a fault.

Surely the only credible reasoning is that there is corrosion/resistance on both the plug and the socket terminals on the left hand wiring plug and the left hand socket.

I don't know the items myself but it/they need careful examination. 'Left field' suggestion. Grinding paste/Brasso on a Q-tip? With everything switched off.

 

[Keefmilbo]

Yes correct, I have examined all connectors and they look pristine. I will clean everything tomorrow. I thought the light unit from the left would work in the right socket but it's as if it's the left light units connectors and the left plugs on the car. I have looked for corrosion and melting but everything looks new but I will clean all connectors tomorrow. Thanks for the reply.

 

[Keefmilbo]

Indicator working this morning so difficult to test, it's intermittent. Cleaned all connectors including one inside light unit going onto pcb. I have also added a wire from before the car plug to after the plug on light unit so completely removing all plugs upto the plug on pcb board in light. If it works for day or two I will remove added wire and check again. I will let you know.

 

[Keefmilbo]

Worked all day today so somethings changed.
Goes to show the merc specialist and Mercedes dealer both wanted to change lamp and wouldn't refund price of lamp if that didn't cure it. It looks like it's a connector issue even though looking at them they look perfect.