SL/R129: Instrument cluster backlight puzzle
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Instrument cluster backlight puzzle
My car is a 1998 sl500.
i upgraded most of the interior lights to LEDs with success, loved the results. When I installed the 4 instrument cluster backlight LED bulbs, 2 worked and the other 2 flickered. I played with the seating and got 3 out of 4 to work, the last one was stubborn and wouldn’t go on. Drove like that for months till it bugged me enough to go back in there. Reversed the polarity on the stubborn bulb (LED sits in the T10 housing) and got it to work but it flickered. Played with the prongs on the T10 that make contact where it sits and it lit up, now had all 4 bulbs working, it was great!
Then Put about 2 hours of driving on the car when the backlights went dark. All 4 of them.
All the other aspects of the instrument cluster continued to work. All the gauges work. All the dummy warning lights, odometer lights, outside temp lights all work. With the headlights turned on, all the other interior lights (radio, heat/AC, console, door panel…) work.
i adjusted the dimmer, that worked.
i checked all the fuses, in the front and in the trunk, all good.
i reinstalled the original non LED backlight bulbs, they didn’t work.
i got a replacement cluster on eBay, taken from same model year R129. installed it and all functions/lights work except the backlights.
I got a second replacement cluster, same thing, no backlights.
i took the car to a good reputation German MB shop, they spent an hour diagnosing. They confirmed power is getting to the pins for the backlights so they concluded the problem is in the instrument cluster board. I gave them a replacement cluster to test, where all worked except backlights. their response was that you can’t trust eBay parts.
I have a problem accepting that, I’m convinced to cluster backlights are not getting power or something in the stream leading there is blown.
i could really use some help here. I don’t know which pins send power to the backlights for manually testing. And I don’t know what behind the firewall coil have possibly blown to cause this.
any help is appreciated.
i upgraded most of the interior lights to LEDs with success, loved the results. When I installed the 4 instrument cluster backlight LED bulbs, 2 worked and the other 2 flickered. I played with the seating and got 3 out of 4 to work, the last one was stubborn and wouldn’t go on. Drove like that for months till it bugged me enough to go back in there. Reversed the polarity on the stubborn bulb (LED sits in the T10 housing) and got it to work but it flickered. Played with the prongs on the T10 that make contact where it sits and it lit up, now had all 4 bulbs working, it was great!
Then Put about 2 hours of driving on the car when the backlights went dark. All 4 of them.
All the other aspects of the instrument cluster continued to work. All the gauges work. All the dummy warning lights, odometer lights, outside temp lights all work. With the headlights turned on, all the other interior lights (radio, heat/AC, console, door panel…) work.
i adjusted the dimmer, that worked.
i checked all the fuses, in the front and in the trunk, all good.
i reinstalled the original non LED backlight bulbs, they didn’t work.
i got a replacement cluster on eBay, taken from same model year R129. installed it and all functions/lights work except the backlights.
I got a second replacement cluster, same thing, no backlights.
i took the car to a good reputation German MB shop, they spent an hour diagnosing. They confirmed power is getting to the pins for the backlights so they concluded the problem is in the instrument cluster board. I gave them a replacement cluster to test, where all worked except backlights. their response was that you can’t trust eBay parts.
I have a problem accepting that, I’m convinced to cluster backlights are not getting power or something in the stream leading there is blown.
i could really use some help here. I don’t know which pins send power to the backlights for manually testing. And I don’t know what behind the firewall coil have possibly blown to cause this.
any help is appreciated.
