Hi all, another small problem to ask about, I'm having some issues with my headlight switch and some stuff related to it.

As w124 owners are aware, our cars have both headlights and foglights. Due to the american headlights being very weak I drive around with my fog lights on as well in order to put out a decent amount of light. Both the headlight and foglight bulbs in the car are newish, less than 6 months old.

The other days driving at night I notice that the indicator light is on about a dead bulb, so I look and see one of the fogs lights is out, no big deal. So it's like that for a couple days, then the other night I go to flip on the fog lights and I notice that the indicator light is now off, which should mean that no bulbs are out. So I go to look at them and now they're both out! I can imagine them both going out, but the indicator light in the gauge pod isn't on, so something, somewhere is in this circuit is bad.

I figure I'll test the bulb connectors with a multimeter to see if there's any power going to them, but other than that I really don't know what it could be. Does anyone know about this kind of stuff?

__________________
1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

Perhaps the indicatior circuitry tests both components of a circuit and if they're different, lights the warning. Both on and both out are equal, of course. Fix your fog lights first before worrying about the lights out system. This is, of course, NOT a headlight switch issue.

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Kent is right on track. The "light-out" indicator measures resistance in each circuit. So if one bulb is burned out and the other is not, the indicator illuminates. If both are burned out, the resistance is the same so the indicator light does not illuminate.

Concerning your practice of using the fog lights to provide more light, I don't think you are achieving any substantial benefit under normal conditions. The fog lights throw their light low, wide, and not very far. I don't think they add very much light down the road in clear conditions. However, I would like to hear from others on this.

regards,
Mark

I do see what the both of you mean, and if the "light-out" indicator measures resistance in each circuit then they both would indeed cancel each other out, making this an easy fix. The only reason why I think this isn't the answer to the problem is because I did have both headlight bulbs out in the past at the same time and I do not recall the "light-out" indicator going out, it stayed on. I'll test the circuit in the next day or so.

As far as driving with the fog lights on, I totally agree with you with all you said. All I can say is that the beam pattern on the headlights is that bad, where the fog lights improve the light output under all conditions. I will go as far as even suggesting that the foglights, on without headlights, are brighter and spread light to a larger, further area than the headlights, making the headlights of no use at all.

__________________
1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

I prefer using the fogs to illuminate the side of the road. I do quite a bit of rural driving and find them to greatly improve nearby road lighting. Frequently have folks flash their lights at me thinking I have high beams illuminated. My bulbs are legal wattage and properly aimed so I know that is not the case. I added the Bosch Euro headlamps a few years ago along with SilverStar bulbs and find that change to be dramatic. May not be the best headlamps I have ever had for reach and pattern but they are much more than satisfactory.

The pitiful light output of the US spec headlights is why so many W124 owners opt for the Euros...not to mention that they are better looking as well...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car