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. http://www.peachparts.com/shopforum/showthread.php?t=232523
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Darren Asuncion
'81 300D Silver Blue metallic
'04 MINI Cooper S, Indi Blue w/ White roof
'94 Jeep Cherokee Sport, Flame Red