redgaucho

Hi, everyone! Let me pick your brain a little bit...

Both the front and rear fog lights are working fine in my 94 C280, but the orange indicator on the switch itself is not coming on. Does anyone know how to replace the bulb inside the switch? I noticed in my Haynes manual wiring diagram that there is such a bulb in there, but how does one get to it? Also, does anyone know what type and size this bugger is?

At some point I would like to modify the rear fog light assembly to allow both the left AND the right side lights to increase in brightness, like the left side does right now. I live in the South, where fog is an almost daily road hazard, and would like to add to my car's visibility for safety...

Any ideas from the experts here?

TIA,

Serge

scorchie

I'm not an expert, but I'll add my opinion...

1) Mercedes only illuminates one rear fog light because this has proven to be safer.

2) If you add another rear fog light by just connecting a wire from the left side to the right side, you will be exceeding the current carrying capability of the wiring harness, for long term use. If you do not have a bulb failure warning on your fog light (it's possible you don't have this in a 1994 car), then you can replace your bulbs with LED bulbs (just for the fog lights) and reduce the required current. Then the single wire would be within spec.

-s-

sph17

You are too modist as many people look to you for definitive advice for their problems.


To replace the small indicator bulb for the rear foglights you need to pull the headlight switch off. You know how the switch pulls to you one click towards you for front fogs and two clicks for front and rear fogs? With the light switch in the off position, just pull it to you and it will pull off the stalk that holds it. It is only held on by friction. You will find a little bulb there that needs to be pulled out and replaced. I do not know what the designation or number is. If you have a MB dealer by you, you could pick one up at the parts counter.

The older MBs (80's) did not have the rear foglights wired, and we had to get bulb holders, reflectors and run a hot lead from the light switch to get rear fogs. MB has alwayse only had one light, where-as other European Co's put two. My feeling is that two bright lights will be mistaken by other dirvers as a "driver riding their brakes." MB has always had the left rear light be the fog, (in countrys where we drive on the right). My thoughts are that they do this so that drivers will know which side to pass on.

Why be like other European Vehicles and have two rear fog lights?

rotorgasm

so people dont always pull you over and tell you "one of your taillights is out."

audi also has one rear fog light. it is common practice for them to add a second one on the right side taillight.

sph17

Good Point! I guess since I have been running only one left rear fog for 20 years, I still like it the old fashion way. Now that it has become "popular" for cars to have them, only MB and Audi seem to have one light. BMW dosn't have it yet. Their Forum has instructions for adding them as the BMW people feel left out and want to be like us.

You can't win. Either the un-informed American drivers either think you are riding your brakes, or have one "brake light" out.

scorchie

Technically, I believe you are not supposed to use your rear fog light if someone is behind you... sort of like a high beam on your headlights.

I'm not sure about the reasoning for this, because then who is there to see it?

-s-

redgaucho

Thanks for the replies, scorchie/sph17 and rotorgasm!!

I will replace the switch indicator bulb asap.

About the rear rt fog light: I noticed that the lt rear fog light uses the same bulb that the (red) parking light uses, but it uses a second element in the bulb. It only comes on if the switch is pulled to the second notch. The brake lights, on the other hand, are separate. So, if I adapt my rear fog lights to work both on the left and rt sides, wouldn't that just increase the brightness/visibility-of-my-car from the rear? The brake lights would still operate normally...

What do you think????

Thanks for your inputs!

Serge

narci

The real reason to add a second rear fog light is to use them if some d00d is tail gating you. Turn on the rear fogs, and it looks like your braking so he'll brake whil you speed off

scorchie

As mentioned before, it will require running two bulbs through the wiring intended for one bulb... which can overheat the wiring if used for extended periods.

-s-

sph17

Did you purchase this car used? I do not think that MB normally uses the bulb you describe in the rear tail light assembly of the W-202. I think someone put the wrong bulb in your rear fog light. I believe that you should be using the same single filiment bulb as your rear brake lights. The bulb you have will work as you describe, but is not made for that location. If you replace the bulb, you may find that it is the same as the bulb in your front turn signals if I remember correctly.

There are 50W bulbs, and also Halogen bulbs made that fit into that type socket for people who want brighter rear lights, but you might melt the plastic lens and reflector, and may draw more amps than the circuit is designed for. Be careful of modifications or alternate bulbs.

scorchie

Thanks for the comments.

I'd add to your helpful instructions, that while you're behind the switch, consider taking a socket and tightening it up. My C43 switch loosened over time so that the switch would rotate slightly... it gives it a nice solid feel to have it tight!

-s-

redgaucho

Thanks to all for your helpful info. For now, I will cease and desist my attempt to have two rear fog lights. I have to research it further. The LED idea seemed feasible...

The headlight switch foglight indicator bulb was replaced easily, as described by y'all and my indy shop had them in stock for $1.09. Probably the cheapest Benz part I will ever buy...

About the left rear fog light bulb specs, I have the same bulb in both the left and right side position/parking lights. They both have 2 elements, though the second one on the rt side is not used, for now... The housing that holds the bulbs has inprinted the type bulb to be used and reading the numbers from the body, they seem to correspond... My car is a 94 C280, and as far as I can tell, these are the spec bulbs... I can't recall the designation right now... What bulbs do u use on your car, sph17?

Thanks again for all your inputs. I am still very green on my first Benz and willingly accept all comments.

What a great forum!!

S.T.

sph17

Silly me. Just because MB did it the way I described with the W123 and the W201, dosn't mean MB wouldn't change their way of doing things. I have to admit I hadn't replaced a rear tail light bulb since geting my first W202 19 months ago. I went out and actually looked and you are correct. There is a two prong bulb in both sides, with both filiments being illuminated on the left when the rear fog light switch activated.

If you want to run a wire across from the left fog light, obtain the miniture female connector and insert it into the one empty socket in the wireing harness plug on the right, you could energize the second filiments on both sides. But remember what scorchie said, you may draw too much current and blow a fuse, so do it at your own peril. As MB has pre-wired the right "fog light bulb" in the light assembly, I assume in some markets they illuminate both bulbs as rear fog lights and there is some way to do it safely. In the olden days MB over engineered cars and I would say that illuminating one extra bulb in a circuit would not cause a problem, but with these newer vehicles I am not so sure about this.

Now if you wanted to be 100% safe you could run a fused hot wire from your battery terminal to a relay you purchase from an auto supply store. Use the left fog light hot wire to energize the relay, and you would be sure not to over draw current on the circuit feeding the left rear fog light bulb. Use the switched side of the relay to power the second filiment of your right "rear fog light bulb".

Good luck.

redgaucho

Thanks, sph17! I really like your relay idea!! I still have some time to contemplate this project before I can actually get to implement whatever I decide... Your relay idea is on the top tier so far.

Thanks again,

S.T.

sph17

The second filiment in the rear foglight bulb is 21 Watts which draws about 1.75 amps on a 12 volt system (actally 1.5V on automobile 14V systems).

I checked some of the fuses on my W123 (easy to get to, and the expanation card for what the fuses covered was self-expanitory), and figured how much current each fuse was passing. My 60W low beam was run though an 8A fuse and at 12V would pull 5A. The other low beam and two fog lights were run though a 16A fuse and pulled about 13A when all three lights are illuminated. It seems like with the older cars, MB figures in about 3A "reserve".

Although my first impression that another bulb wouldn't be that big a deal added to the circuit, another 1.75A draw if you only have 3A "extra" capacity on the circuit is getting too close to maxing out for me. The relay probably is the best way to go.

Good luck.

scorchie

Also remember that the fuse is usually there to protect the wiring... the single wire running to the rear fog light is either a 1.0mm or .75mm (can't remember which), but I do know that generally the acceptable limit for .75mm and 1.0mm current over extended periods when carried in a wire bundle is 1.5A and 2.5A.

So, doubling the draw would obviously exceed this rating.

I believe that in newer cars, there is a huge compromise on Mercedes' parts because everything needs to be engineered to last, but also the requirements of fuel economy and emissions drive a very aggressive weight reduction program. Thus, wiring is no longer larger than it needs to be. And the fibre optic cable that Mercedes uses for its telematics... it may seem cool, or we may think it sucks when it's time to add an aftermarket CD changer... but in reality, it lowers the weight of the car by 30-40 lbs.

-s-

sph17

Another big no-no is putting in a higher rated fuse, when the correct fuse keeps blowing. It may "save" you from replacing the fuse again, but may cause a fire. You should realy figure out why the fuse is blowing.

The main wire coming out of the fuse is only as big as it needs to be. A wire feeding a 10A circuit is thiner than a wire feeding a 20A. If you put a 20A fuse into a 10A circuit, and that wire starts passing twice as much amperage as it was designed to do, it can heat up, melt the insulation and concievably cause a fire.

Fuses are your friends. They are designed to protect your car, Not infuriate you because they keep blowing when some electrical component starts drawing more current that it was designed to do (or because you added something that draws too much current).

cheers.