LED bulbs heads up, and Dash bulb warning light question - PeachParts Mercedes-Benz Forum

jbach36 · #1 04-04-2019, 01:05 PM

UPDATE...... Problem found. It WAS the new exterior brake light LED bulbs causing the error light.

I recently changed out the LED bulbs in my 1991 300d w124. I got my bulbs from SuperBrightLED's but there were soooo many problems along the way with them sending wrong bulbs multiple times, that unless you really need to change yours, I wouldn't recommend it.

Yes, the LED's are nicer but this has taken over the course of 2 months to complete the job with bulbs, wrong bulbs, returns, waiting for the "right" bulbs, more returns, more waiting, and a lot of work ripping out the speedometer cluster and especially replacing the bulb in the center dash.

Next up, I used to get an exterior bulb warning light "from time time" before I did the LED dash lights. It was almost always a rear side marker bulb causing the problem. Never with the key in just ACC position, only when the car is started and the lights are turned on. I cleaned the calcium type buildup off the bulb holders long ago and put dielectric grease on the bulb base for better connection and still the dash warning light would come on "from time to time". But I checked all the exterior bulbs and brakes lights and....everything seems to be working.

I replaced the brake lights with LED bulbs about a month ago and I haven't had the dash warning light come since then but maybe the "from time to time" time hadn't hit yet.

Just last night, I put the new speedometer cluster LED bulbs in, turned the key to ACC position to check that they were working, then took the car for a spin. Even with the headlights OFF, I got the warning light just upon starting the car.

I don't know if this is caused by the interior LED cluster bulbs that I just put in. In theory, I don't think the interior bulbs can cause the exterior bulb warning light to come on. If all the exterior bulbs appear to be working, and even with the lights off, why am I getting this exterior bulb error light?

What is causing this problem?

Thanks,

jeff 1991 300d 220k

Maximan1 · #2 04-04-2019, 01:15 PM

Which warning light? Ground issues can make for some weird symptoms.

jbach36 · #3 04-04-2019, 01:21 PM

I clarified my post. The one that tells you an exterior bulb is out. But even with the light switch off, as soon as I start the car, the "bulb out" warning light turns on.

Someone said I might need to install a resistor or something because the LED lights are pulling less electric, but someone else said the interior dash bulbs can't make the exterior "bulb out" warning come on.

Diseasel300 · #4 04-04-2019, 11:08 PM

The exterior warning module doesn't monitor the interior lights or the dash. It only monitors the exterior bulbs. The status of the bulb is only checked when it is activated, so if you haven't turned on the lights, it isn't monitoring those circuits. Brake lights would be the next thing to check, especially since you probably have your foot on the brake when you start the car.

Maximan1 · #5 04-04-2019, 11:11 PM

Perhaps a license plate light or other running light?

jbach36 · #6 04-05-2019, 01:43 AM

Quote:

Originally Posted by Maximan1

Perhaps a license plate light or other running light?

I get the error message when the car is started, no lights turned on yet.

jay_bob · #7 04-05-2019, 07:13 AM

The bulb monitor also has a bad habit of failing internally. It is the longest relay in the box.

I had this problem with the right front marker light, finally traced it down to an open circuit inside the lamp monitor.

Get a hold of the schematic or you will be going crazy trying to find it.