DaveS74

What’s up fellas. Coming from BMW world here, first time MB owner. Looking for the tech gurus out there on this one. Fitted LED bulbs for the low beams yesterday. I expected an issue with check control messages warnings but not this one. Initially the car threw the bulb out warning and wouldn’t illuminate either LED. Checked power supply at the bulb during and had 12v. So I cycled the key and then they came on. But after a few minutes they start to do this routine of shutting off then coming back on one at a time. I was a BMW tech for 15yrs so I’m familiar with the electrical system not liking LED’s. Dealt with this in the past but a BMW wont pull voltage, just throw the error message. Easily addressed with Carly etc. Just shut off the hot and cold check in the light control module. But I’m reading Mercedes doesn’t have this functionality for coding or apps available to do it?
So I guess my options are:
A) Wire in a resistor to trick the car that a filament bulb is installed. Has its issues, heat/melting sht being one of them.
B) Merge the low beam circuit with either the turn signal, parking lights, or fog lights, and hopefully the total resistance of the circuit is enough to satisfy the car. Obviously this will entail any of those lights being illuminated also while the low beams are on.
Anyone have an option “C”?
Thanks.

CaliBenzDriver

You want to upgrade the HL from bulb to LED beam.

I haven't messed with exactly this issue to test solution. Some hands-on research needed.

I liked you software solution a lot and if that's not available then well go to the hardware side...

Replace the SAM measurements RESISTOR to match reading between LED vs. bulb.
This precision power resistor is called a serial shunt.
Pulling front SAM requires a bit of patience you've gained with BMW experience.

Lets say with 1/10th the load current we want same delta-V in the shunt...
So your R value needs to go up by the same factor you're decreasing current.

DaveS74

So what I did today was using test leads, hook a blower motor resistor to the circuit which specs out at 120ohm. Didn’t make any difference. So then I hooked the H7 halogen bulb up instead of the resistor and the LED worked correctly. So it’s not a matter of simply adding resistance to the circuit, I believe it’s current draw the car is looking for. So I went over Autozone and got a pack of Sylvania load stabilizers, 5W/6ohm and they worked like a charm. Only potential issue I see is they get extremely hot. So I made some aluminum brackets and bolted them to the upper support hanging down far enough to get airflow over them through the grill. They make a H7 resistor pack which plugs into the harness and then to the bulb which makes wiring unnecessary. I should have know better and just ordered them with the LED’s but I didn’t think the car would cut power, figured just at worst get a check lamp message.

CaliBenzDriver

You bet it's hot !!

Your 5W Max resistor is dissipating 32W at 14V with 2Amps.

If resistor goes open while you're driving, SAM will switch off HL into darkness.

It's in your best interest to size your upgrade well.
✌️
Your ballast resistor needs to produce as much heat as the previous light bulb used power.

DaveS74

They were right next to all the LED headlight bulbs, was the only rating they had and I believe make. How hot you think that H7 bulb gets? Pretty damn hot lol. I’m willing to bet I could get away with a lower watt resistor. The car wasn’t giving me a bulb out message, was just messing with the power supply.

CaliBenzDriver

I think H7 around 40W... a lot of heat.

Plan B is biild a 4x serial to parallel bridge

DaveS74

They make a resistor pack that plugs right into the headlight connector and the bulb. They’re like $25 on Amazon. Not even worth messing around. Only reason I didn’t go this way Was because I wanted it fixed that day and didn’t want to wait for shipping.

CaliBenzDriver

That's worth it for the troubles it saves.

Can you post a link or pics for the next person converting.

I already have LED HL and think they are the best light available. Grandma bulbs put out scattered light compared to directional LED's.

DaveS74

The resistors I used are made by Sylvania and called “Load Stabilizers”. They’re about 2in long gold colored looking things. The H7 adapter harness can be found on Amazon, search “H7 LED resistor” or “H7 LED Canbus decoder”.

What did you do with your lights to address this issue?

CaliBenzDriver

That's a pretty good solution to get LED without too much headaches.

I ordered my car with the static LED options that don't move at all for sake of reliability. I've been familiar with MTBF managed quality for couple decades.

HL Module components


Module top side


oxidized internal connection

Not saying anything negative about these awesome light projectors - Complete with programming bugs from factory.