Mercedes Benz W123 Lighting Upgrade
Coming soon: daylight with the flick of a switch


I'll be running the 240D in a local rally on November 18, 2000 and I've decided the head lights in the car are not going to cut it in the middle of the woods. So, I'll be modifying the original light fixtures and wiring to support high wattage European code lamps. You can use this page for ideas about upgrading you own car, but keep in mind that bright head lights are not only annoying to other drivers, they can be dangerous!

Note: Any modifications made by following the information on this page are to be done at your own risk! Electricity is a nasty thing. A 12 volt car battery easily melt the insulation off a wire and turn it into a smoldering flaming mess in a matter of seconds. This isn't a good thing under the dashboard of your car! Respect electricity and be sure to use only the highest quality parts available. You don't want to be left stranded without lights, or worse, with a fire.

Stage Zero: E-code lights

I call this stage zero because I think every car out there with sealed beams deserves e-code lights. Installing them is as simple as replacing a sealed beam, and alignment. Lights usually come with 55/60 watt H4 bulbs. This is a standard wattage for lights and the original wiring can be used. The difference is amazing, they're well worth the money. Below are pictures of two common 7" lights. I have a set of Hellas but I'd like to try the Cibies for comparison. You can see the lens is much more interesting. I've been using the Hellas since December 1999 with standard bulbs and wiring. Click here to see how they light up the road.

Hella Flat Lens 7" H4

Cibie Convex Lens 7" with City light


Stage One: Fog light modification

A stock W123 is wired to supply power to the fog light switch only when the low beams are on. This doesn't do you much good in dense fog or snow, since the bright white light will defeat the yellow (or white) fogs. This is especially true with the Hella H4s. By changing the power supply for the fogs, you can run them anytime you like, even with the high beams. The power is fed by fuse number 11, which is a 16A (red) fuse. It also powers the right side low beam. By changing the power source to fuse 3 (left side tail lights), the fog lights have power with the parking light position on the switch.

Removing the fuse panel to make this change can be a little intimidating. Be sure you DISCONNECT the battery first! There is only one nut holding the panel in, and with a little work you can pull the panel out of it's hole. It helps to remove the under-dash cover in the drivers side foot well. Be careful, damage to the wiring or fuse panel can be expensive to fix!

You'll notice that to get to the connections to the upper row of fuses, you need to removed the connections to the opposite fuse in the lower row. Make sure you remember where these wires belong and don't loose the screws! A magnetic tip screw driver is a must. The power for the fogs is gray with green and yellow marks. Clip the wire and use tape or some shrink wrap tubing to cover any of the wire that remains exposed. Carefully crimp a new ring connector on the fog light wire and protect it with another piece of shrink warp. Then connect the wire to fuse number three, removing any wires you need to to gain access. The last step is to change the fuses. Swap the 16A from 11 with the 8A from 3. The fogs draw a lot of current, almost 8A by themselves. Of course you won't have to worry about the current draw if you move to stage two! To help identify wires, you might want to get a copy of a Chiltons manual. They have a seperate schematic for the lighting system which is very useful.

Click here to see the results of Stage One.

Stage Two: Relays:

With the rally one week away, I installed relays to allow me to run higher wattage bulbs without worry. This step takes a little planning to make sure the connections made are not only correct, but safe! I decided that I would install OEM style (30A) relays in the empty spaces of the stock relay box to ensure an original looking installation and easy to follow wiring. With parts I collected from the junk yard, I was able to make wiring harnesses that just plugged into the wiring harness for the head lamp assembly to power the relays. The harnesses also have 10 guage wire to runing to the battery, and to sockets in the headlights. I have four relays in my system, left low, left high, right low, right high. To keep the wires running across the engine compartment to a minimum, I installed another OE relay box on the passenger side of the car. I'm very satisfed with the final results. I used high quality fuse holders, crimp connectors, wire, shrink wrap tubing, and all of the original style harnesses have wire carefully soldered to the pins. It took a few hours to make each one. If I want to go back to the stock setup, I just need to install the old blubs and wiring inside the lamp assembly, disconnect the relays from the harness and plug it back in. You can run an extra set of relays for the fog lights, but I removed them and added additional high beams, see the next stage.

Original drivers side relay box with the two new headlight relays

A relay socket

Installed passenger side relay box
Four empty spaces... hmmm....

The new box with cover


Stage Three: Driving Lights

With relays installed (or while installing them), you can easily add an additional lamp to the high beam circuits. I've found that a set of e-code 5 3/4" H1 high beams (Cibies in my case) fit very nicely in place of the factory fogs with only, um, slight modification! The hole in the back of the aluminum cup that holds the fog light in place isn't large enough for the back of the new light to fit through. Not a problem when you have a lathe around:

The housing on the lathe

After, and before

The final hole ended up being about 2.6 inches. Of course, install them with high wattage bulbs (I have 85's in there now) and be sure the aim them carfully (this may take a few days). The fog light switch now has no effect, but can easily be used to control fogs under the bumber in the future.

The spring on these cups can be a real pain to install (and staring at it like this doesn't help). Put the spring in the frame first, then pull in onto the cup.

Nice clean looking lights! And a perfect fit!

Lights on

Lights off... they sorta have a euro look....

Click here to see what these lights look like (high beams 80/100w H4s, 85w H1s)

Better pictures of the beams coming soon


Last update November 12, 2000

Since November 4, 2000