W164 brake lights

[tlynch]

I have a 2010 ML350 Bluetec. Recently the dash displayed messages regarding rear brake lights, and I dove in.

I thought I would seize the opportunity to go LED for the rear brake lamps. This worked in 75% of the locations. For the passenger side rear main brake light, an LED bulb will not work. A conventional bulb in that spot works. I tested the LED bulbs that I tried in other locations, and they worked.

This is confusing. I am aware of the repair kit with the extra grounding wire, and I can certainly install that if needed. I just expected that if a conventional bulb worked in that socket, then an LED lamp should as well.

Does anyone have a good explanation for why a known good LED brake lamp won't work when a filament bulb does?

Thanks!
Tom

[Sugar Bear]

Don't know why it won't light but...have read and IIRC experienced that the brake light bulbs should be EXACT OE or OEM equivalents, otherwise the cruise control won't work. It's something about the circuit reading a different resistance value from other types of bulbs...may want to leave OE bulbs in the brake lights.

Good luck!!!

[tlynch]

Originally Posted by Sugar Bear

Don't know why it won't light but...have read and IIRC experienced that the brake light bulbs should be EXACT OE or OEM equivalents, otherwise the cruise control won't work. It's something about the circuit reading a different resistance value from other types of bulbs...may want to leave OE bulbs in the brake lights.

Good luck!!!

Interesting. I have not noticed an issue with cruise control.


Thanks for the response.
Tom

[ILUVMILS]

The rear SAM fires the stop lamps on the 164. LED’s don’t load the circuit properly so the SAM thinks there’s a malfunction and kills the circuit.....

[tlynch]

Originally Posted by ILUVMILS

The rear SAM fires the stop lamps on the 164. LED’s don’t load the circuit properly so the SAM thinks there’s a malfunction and kills the circuit.....

Good to know.

The part that puzzles me most is that an LED lamp is in place on the driver's side and works beautifully, while an LED lamp on the right does not work at all.

Why the difference from side to side? Why does the SAM fire one LED lamp but not another identical lamp?

Thanks,
Tom