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I had my SLK 55 inspected today (state vehicle inspection). I knew I had a front fog light light out. The mechanic indicated that a rear bulb was out also, which it was. I reviewed the manual and the top left rear bulb (left only, not right) is the rear fog light that comes on when the front fogs are activated. What's the purpose of the top rear light. I tried every combination and it won't light.

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SiLK

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It shouldn't work!
Most new vehicles use only one rear fog light at the driver's side.
I don't exactly know why though!

mtiede

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So, are they trying to replace the bulb that isn't meant to work?

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Yes, the first thought was the bulb was burnt out. I swapped the bulb out. Only the left side is illuminated when front fogs are on. Why would MB install a bulb on the left side, with contacts, if it's non-functional. Is the right side bulb used for any other purpose?

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HwoALanG

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you get to be kidding me... so my passenger side fog light doesn't work? wow...

DansSlk

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Because in works in other countries, like here in the UK the rears are activated separately and they both light.

The reason they install everything is to keep production options down otherwise they would need two types of light cluster for the car, i don't know why your mechanic picked it out as faulty i guess they don't work for MB otherwise they really should know.

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etyu

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Is there a way to make them (right and left rear fog lights) light up for US spec vehicles? perhaps via DAS?

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Eddy

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Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package
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Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, Mod. R170 ant., EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, bilateral rear fog lamps enabled.

DansSlk

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The light switch is hardwired to the driver SAM and its calling the shots, it will have a setting to change this and it will probably have just 2 options something like US / ROW (Rest Of World).

I will have a look for you later on, you might need a new light switch because the rear fogs are activated separately.

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nmslk

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I had asked the same question a few months back about trying to get both left and right side rear fogs to would on my US spec car. NoRegrets said the SAM wouldn't allow it but if you figure out a way that would be wonderful.

I turn on my dual sided fogs on my Volvo to get someone tailgating me off my rear at times.

I'd love that option on the SLK.

-M

VitaminT

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Yeah on my switch I pull it out to the first notch for the front fogs and the second notch for the fronts and single rear.

I never have used it as my brother told me it just made it look like there was something wrong with the other side.

noregret4life

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another reason why the rear right fog light is installed, yet not working in the US, is because of the lighting system's ability to substitute bulbs in case of a malfunction.

Keeping in mind if your turn signal goes out, it will use another bulb as your turn signal in the rear. So using a priority system the lighting computer steps down to the next bulb on the list, if thats not working either, then the next one down... and so on.

As for activating it... Dan could advise on the "proper MB" way of doing it.
I've been looking into working on a project for the rear tail lamps to activate the additional fog light, activate the reverse lights when unlocking the car (just like fog/lowbeams for everyone), and some other additional options. Just tough to find correct connectors and not slice into any wiring.... we'll see though, a project for this summer.

Dolebludger

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What an interesting post! After reading it, I went out to see what the '07 280 did about this. US spec. One pull out on the light control in the fog light position and only the fronts come on. two pulls out and the fronts and the red rear driver's side fog light comes on, but not the passenger's side. Did someone have too much beer when he designed this? There looks like there is a bulb to illuminate the pax side red rear fog light, but does not work.

Where I live, we do have fog. DanSLK, what would happen if we merely ran wires from the driver's side rear fog light to the pax side? Would that work, or would we blow fuses, fry computers, and the like?

noregret4life

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I ran wires on my R170 rear fog lights to get both to light up, but the R170 didn't have a bulb, socket, or wiring to it.

I'm sure Dan will confirm this, but the only real "safe" way to wire in the pass side rear fog light is to isolate it entirely from the Lighting computer aka rear SAM. Otherwise you are sending power in reverse back to the computer from the bulb and thats a big no no in MB wiring world.

If the socket however is completely isolated, its just a matter of tapping wires and running it (as i did on the R170). However from my nosing around, its a pain getting the socket isolated unless you clip wires, or clip connections in the tail lights themselves.

So in order to NOT send power back to the lighting computer, you need to install a DIODE on the line from the socket to the lighting computer. Diodes allow power to flow only in 1 direction, and block the other. But that would mean cutting wires and soldering this into the stock harness.

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Thanks to everyone for the great info. I took my car to a local (non MB) shop for the state inspection. He didn't know, and I wasn't familiar with the rear fog light system (left side only), until I reviewed the owners manual. Curious, wouldn't two rear fog lights be better than one, since the light is in place?

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mtiede

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Just guessing, but maybe there is only one so that the car can be seen from the rear in fog, but having 2 on might sort of blind the guy behind you in the fog?

noregret4life

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I think that MB is trying to stay away from 2 bright red beams on the rear to no confuse drivers with brake lights.

In the rest of the world, rear fog lights are already a feature constantly seen on the roads. However the US is a little behind, and people may get "confused".

I also think they are going on the notion of how people always tend to pick out "faults" in others, and in this case, they say "Hey look his rear light is out!" -but reality by then they already have noticed you on the road in comparison to someone who does not have fog lights at all.

DansSlk

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I had a quick look and if you change the SAM's from US mode then it should work, the issue thats springs to mind is you guys have side markers and if you where to change a lighting setting away from US the SAM's might not bother to power them anymore.

About the worst case well i guess its wiring or computer damage but i think a more realistic worse case issue is both of the fogs failing to light after you mod them, like Lenny said its all about hiding from the SAM the fact thats its powering 2 lights and not one.

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nmslk

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So when you say change the SAM is that the actual wiring or just the software?

-nmslk

coolboarder

Actually I think most if not all European imports deploy single rear fog lamp for the US market and it is the choice of the manufacturer:

(ECE Regulation 38, SAE J1319) In Europe and other countries adhering to ECE Regulation 48, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which are switched on manually by the driver in conditions of poor visibility to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog lamp is 150 to 300 candelas, which is within the range of a U.S. brake lamp. For this reason, many European vehicles imported to the United States have their rear fog lamps wired as brake lamps, since their European-specification brake lamps may not be sufficiently intense to comply with U.S. regulations, and in North America rear fog lamps are not required equipment. However, they are permitted, and are found almost exclusively on European-brand vehicles in North America — Audi, Jaguar, Mercedes, MINI, Range Rover, and Volvo provide functional rear fog lights on their North American models.

Most jurisdictions permit rear fog lamps to be installed either singly or in pairs. If a single rear fog is fitted, most jurisdictions require it to be located at or to the driver's side of the vehicle's centreline — whichever side is the prevailing driver's side in the country in which the vehicle is registered. This is to maximise the sight line of following drivers to the rear fog lamp. If two rear fog lamps are fitted, they must be symmetrical with respect to the vehicle's centreline. Proponents of twin rear fog lamps say two lamps provide vehicle distance information not available from a single lamp. Proponents of the single rear fog lamp say dual rear fog lamps closely mimic the appearance of illuminated brake lamps (which are mandatorily installed in pairs), reducing the conspicuity of the brake lamps' message when the rear fogs are activated. To provide some safeguard against rear fog lamps' masking of brake lamps, ECE R48 requires a separation of at least 10 cm between the closest illuminated edges of any brake lamp and any rear fog lamp.

DansSlk

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nmslk, Its just software.

A few settings.

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