Fog light wiring modification (US wiring to Euro wiring) - PeachParts Mercedes-Benz Forum

iq678 · #1 09-10-2008, 03:48 AM

Hey everyone -

I've decided that I hate how US-market w123s are wired - specifically how we are NOT allowed to run the foglights with just the parking lights, or with high beams. I found out that European-market (and perhaps rest-of-the-world) vehicles allow the fog lights to operate with the low beams, high beams, and with just the parking lights.

I spent a lot of time last night studying differences between US and Euro wiring, and this is what I learned:
US models: fog light feed comes from Fuse 11.
ECE models: fog light feed comes from Fuse 5. Fuse 5 is powered from the same source as Fuse 3.
Interestingly enough, Fuse 5 is unused on US models (or at least on my '81 300D).

So, today's project involved modifying my car's wiring to mimic the set up on Euro models.

Disclaimer: Yeah, I'm very well aware that some states do not allow this sort of functionality, and how high beams aren't supposed to be used in the fog - so *please* do NOT bring that sort of discussion into this thread. I am simply posting here to provide information, as I know some people want the same sort of lighting functionality built-in on Euro models. If you decide to take on this project on your own car, you are doing so at your own risk. Please look into your local laws to see if such a modification is legal in your area.

Tools/supplies needed:
Electrical diagram
Phillips screwdriver (magnetic tip is REALLY handy here)
8mm nut driver
Wire crimpers
Wire strippers (mechanized ones are a plus)
M4 x 10mm screws. Qty: 2 (good idea to have more, in case you drop/lose some)
M4 lock washers. Qty: 2 (good idea to have more, in case you drop/lose some)
Good quality electrical wire (for use as a jumper between Fuse 3 and 5). I used 12-gauge.
Ring terminals. Qty: 4 Use correct size for M4 screws, and the wire you'll be using.
Electrical tape
Some patience, and perhaps a good friend to lend a helping hand.

Step 1: Unplug battery

Step 2: Remove knee bolster, driver's side (sorry, no pic)

Step 3: Remove cover for fuse box, remove retaining nut and washer (8mm), then push fuse box into the cabin. Then push fuse box back into the engine compartment at an angle, so you can access the back side of the fuse box. It's a tight fit, but if you're careful, you can do it!

Step 4: Locate the foglight feed wire on the back of the fuse box (this wire runs to the NSE terminal on the headlight switch). It is gray w/ a green tracer and yellow dots. It will be connected to the lower terminal of Fuse 11, crimped into a ring terminal with another wire (yellow), which feeds the right side low beam headlight. Cut the ring terminal off these two wires, strip them, and install new ring terminals. Reinstall the yellow wire back on the lower terminal of Fuse 11. Reroute the foglight feed wire over to Fuse 5. You may need to remove wires to gain access to the fuse terminals.

Step 5: Make a jumper wire to supply power to Fuse 5 from Fuse 3. Screw one side to the upper terminal of Fuse 3. Screw the other side to the upper terminal of Fuse 5.

Step 6: Screw the foglight feed wire from Step 4 into the lower terminal of Fuse 5. Don't forget to screw down wires in their appropriate places, if you had to remove any to gain access.

Step 7: Push the fuse box back into the cabin, then reinstall back into its normal spot. A helper might come in handy for this step, as the fuse box wants to fall back into the cabin. Tighten down the 8mm nut (don't forget the washer). Install fuse (8 amp) if there isn't one already there. Reinstall fuse box door. If you are running fog lights that are more powerful than stock, you may need to install a bigger fuse. 8 amp is what appeared to be used on the Euro models, according to the wire diagram I looked at.

Step 8: Put the car back together - driver's side knee bolster, connect battery, reset clock/radio, etc.

Step 9: Enjoy being able to use the fog lights how you want!

With just the parking lights (city lights in my case):

With the low beams (this was the only way fog lights would turn on before)

And with high beams (Not a good idea in fog, but could help visibility on windy, unlit roads)

If you have any questions, please feel free to ask! Hope you enjoyed this!

Look here for my next project: Wire up the rear fog lights and get them working w/ the stock headlight switch. How-to: Get the rear foglight(s) working on a US w123 (links to photos)
__________________________________
Darren Asuncion
'81 300D Silver Blue metallic
'04 MINI Cooper S, Indi Blue w/ White roof
'94 Jeep Cherokee Sport, Flame Red

JHogan · #2 09-10-2008, 05:58 AM

I will do this mod. Well documented and neat work.

Thanks again,
Jay

2.5Turbo · #3 09-10-2008, 11:52 AM

Interesting that the 123's don't let you do these things. My '90 124 lets you have the fogs on regardless of what light setting you're on, except the left and right parking settings and off.

TX76513 · #4 09-10-2008, 11:59 AM

Very nice documentation. Mods need to stick this thread in the DIY tab.

MarkM · #5 11-07-2008, 08:21 AM

This writeup was great....I have been trying to think of something that I could tinker with this upcoming weekend, and this fits the bill! I have hated that way fog lights were linked only to low beams. Thanks.

Another question...about front corner lights (directional, running lights). In my 84 123 wagon, I changed my original US headlights to euro like yours, but I chose not to use the euro "corner lights" because these are 2-pin lights and function only as directionals, relying on the "city lights" inside the headlight as "running lights". (I hope my terminology is understandable!). In the US configuration, 3-pin corner lights function as both directionals and running lights.

I like haveing the corners on as running lights, as well as directionals, so when I installed the euro headlights, I modified the wiring to allow me to use the original US corners. So when I put on running lights, both the city lights inside the headlight housing and the corners are lit.

Here is my question: Is there a good reason to use only city lights as running lights, and use corners only as directionals (euro configuration)?

(I would like to change to clear corners, but they only come in euro two pin style....if I want to use clear corners for both running lights and directionals, I would have to install 3-pin light sockets, but the 3-pin US sockets do not fit into the clear euro corners).

Thanks again for the pictoral about fogs...

Mark

iq678 · #6 11-07-2008, 12:26 PM

With my Euro corner lights (Bosch), I simply swapped the 2-pin bulb holder with the 3-pin holder. Interestingly enough, the 2-pin bulb holder also screwed into the US corner light - so I figured the 'hole' was the same. I'm thinking that there might be a difference in the bulb holder design between the different years of w123.

I could not use the 2-pin bulb holder without modifying the existing 3-pin plug, so it was just easier for me to swap the 3-pin bulb holder and reroute the running light feed over to the city light. It would be super easy to get the running light functionality back on the corner light if I decide I need it - just run a wire back to the 3rd terminal on the bulb holder.

The reason why I decided to go with the Euro configuration for lighting: I simply wanted my car to be more like a real Euro-market vehicle. With that said, I've been told by my friends that the turn signals are much more distinct and noticeable in this configuration. Perhaps this is the reason why my '95 Land Rover Discovery (US market) was wired up in a very similar fashion. Land Rover decided to add a separate sidemarker light on the bumper end, instead of putting the running light in the corner light assembly.

I do like having the city light function. It seems safer in the event that a headlight burns out, as oncoming traffic will still see the width of the vehicle. Kinda wish more cars in the US would come equipped with these city lights. Land Rover also elected to keep the city light for US models (yay!)

Hope this helps!

pj67coll · #7 11-07-2008, 02:04 PM

Interesting write up. But I have to ask. Why the hell would anyone ever want to use foglights with high beams? I had occassion to use the fog lights often on my 116 many years ago. They were fantastic. I'd go so far as to say I was in the safest car on the road in my area both in terms of seeing and being seen. But using high beams in that fog simply created a overpowering white out type glare that basically blinded me an made it impossible to drive. I would never use high beams in fog.

- Peter.

Chad300tdt · #8 11-07-2008, 02:11 PM

I'm interested in fogs with high beams not for fog driving, but to get me closer to the brightness of newer cars. Even with my H4s, the headlights on bright aren't nearly as bright as the low beams on the 2003 Acura TL-S I recently sold. It seems that the low beams with fogs are equal to the high beams, so I figured high beams with fogs would be even brighter.

iq678 · #9 11-07-2008, 03:03 PM

I would never think of using the high beams in fog or snow. Anyone with common sense will realize that high beams just don't work in these conditions. Additionally, I just don't like it when something is rigged in a way to prevent me from doing so, especially if there are still good reasons to be able to have this functionality.

There is some practicality to using high beams + fog lights, which is my main reason for this mod. It is extremely dark in rural Alaska in the winter, and most of our roads are not lit. Low beams are usually ineffective on windy roads (even if you have Euro spec lights), so you end up driving with the high beams. In doing so, you lose peripheral vision due to the lack of width of the high beams. The fog lights have a very wide pattern, and help illuminate the edges of the road. This complements the narrow pattern of the high beams. With all the wildlife here that could jump out unexpectedly, I feel that this combo of lighting is actually safer than the default US setup.

w123's are rare enough around here, I don't want to risk crashing mine because of some mandated fog light "lockout" that I could easily bypass.

Quote:

Originally Posted by pj67coll

Interesting write up. But I have to ask. Why the hell would anyone ever want to use foglights with high beams? I had occassion to use the fog lights often on my 116 many years ago. They were fantastic. I'd go so far as to say I was in the safest car on the road in my area both in terms of seeing and being seen. But using high beams in that fog simply created a overpowering white out type glare that basically blinded me an made it impossible to drive. I would never use high beams in fog.

- Peter.

TheDon · #10 11-07-2008, 03:06 PM

Looks like I've got something to do this weekend

Chad300tdt · #11 11-07-2008, 03:11 PM

Mbeige also said that bulbs from w126 and w116 map lights will fit in the socket for the city light. They are brighter and whiter and no more wattage, just a different shaped bulb and possibly gas filled.

Does anyone know the bulb number for the map lights? I'd like to put them in my Bosch Euros.

iq678 · #12 11-07-2008, 03:13 PM

Something that really helped out the H4 conversion on my Jeep Cherokee - the use of relays for the headlights. It was amazing how much brighter the lights were once I completed the relay setup on it.

I'm thinking of doing something similar with my 300D, as I'm sure there's quite a bit of voltage drop in the headlight wiring.

Quote:

Originally Posted by Chad300tdt

I'm interested in fogs with high beams not for fog driving, but to get me closer to the brightness of newer cars. Even with my H4s, the headlights on bright aren't nearly as bright as the low beams on the 2003 Acura TL-S I recently sold. It seems that the low beams with fogs are equal to the high beams, so I figured high beams with fogs would be even brighter.

pj67coll · #13 11-07-2008, 10:46 PM

Quote:

Originally Posted by iq678

I would never think of using the high beams in fog or snow. Anyone with common sense will realize that high beams just don't work in these conditions. Additionally, I just don't like it when something is rigged in a way to prevent me from doing so, especially if there are still good reasons to be able to have this functionality.

There is some practicality to using high beams + fog lights, which is my main reason for this mod. It is extremely dark in rural Alaska in the winter, and most of our roads are not lit. Low beams are usually ineffective on windy roads (even if you have Euro spec lights), so you end up driving with the high beams. In doing so, you lose peripheral vision due to the lack of width of the high beams. The fog lights have a very wide pattern, and help illuminate the edges of the road. This complements the narrow pattern of the high beams. With all the wildlife here that could jump out unexpectedly, I feel that this combo of lighting is actually safer than the default US setup.

w123's are rare enough around here, I don't want to risk crashing mine because of some mandated fog light "lockout" that I could easily bypass.

Sorry. I didn't see the picture where you captioned it that you were not doing this to use high beams in fog or snow. I was posting from work and all the pictures were blocked by our filter. I better understand what you mean now. Indeed the fogs do provide an excellent wide dispersal of light to enable you to see the sides of the roads well in adverse conditions so you might be on to something for your application.

- Peter.

ARINUTS · #14 11-07-2008, 10:54 PM

anyone know if the procedure is the same on a 83 w126?

compu_85 · #15 11-07-2008, 11:06 PM

I like to leave the fogs on all the time on my W126, they illuminate the edges of the road where deer like to hide.

-Jason