I want to operate fog lights without headlights

[Robby Ackerman]

My '85 190E 2.3-16 allows separate use of fog lights and head lights or both at the same time. My '83 300 D light switch will operate the fog lights only in conjunction with the low beam headlights. How do I modifiy the 300 D switch/wiring so that turning it clockwise one position and pulling it out will operate the fog lights without the headlights? I used the forum search function and found 287 threads dealing with lighting but didn't find this question.

[jjrodger]

Why would you want to do this?

You could simply remove the side light bulbs, although this will mean you are without parking lights/side lights.

[Robby Ackerman]

Jonathan

On my 190 E 2.3-16 I use the fog lights as my DRLs. Also the fog lights run independent of the headlights on every other car I own and have owned, except on both my 300 Ds the headlight switch is wired differently so that the fog lights come on only after turning on the headlights.

A friend has is the 16 valve on a trip ... when it returns I could look at the wiring on the 16 valve and 300 D switch and see how they differ. However, if someone has already been there, done that, I'd appreciate learning from them.

Robby

Bobby,

I use fogs on my 81 300D as DL's. On my 126, I can turn the switch one click clockwise and pull it out to operate fogs without headlights (parking lights work, also). I removed the switch on the 123 and in vestigated possibility of modifying the wiring to work like the 126, but I was unable to do so. I determined which terminal powers which lights, etc. I was hoping I would be able to merely move or add a jumper wire or two simply on the switch. Finally, I ran a wire (to close the relay) from parking light terminal (one click clockwise) to a new relay in the relay box on top of left front wheel well; then I ran a wire from the relay back to the parking light terminal on the switch to operate the fogs. I think I got power for the relay/fogs from appropriate size fuse in fuse box. It has been about a year since I did this. I may have forgotten some of the details. Wish I had drawn a diagram, etc. Investigate the switch; I think you'll see how you can do it.

[Robby Ackerman]

Wilton

Thanks! I like the simplicity of your idea. I understand how to do what you described without all the details. Today I'm working on my 190 SL. last year I drove it to Alaska and back and its never been quite the same since, ha! A lot of custom machined items vibrated off and I'm finishing the couple odd items that are left. This evening or tomorrow I'll tackle the fogs, thanks again!

Robby
newport news, va

Bobby,

Did I read about your trip in Star, or where? Great trip and written account of it! 'Enjoyed it!
My wiring setup on the 123 to use fogs as DRL's was very simple and easy to do after I figured out purpose of each terminal on the switch. I was hoping I'd find one that would go "hot" when the switch is pulled out, like the 126, but I did not. Good luck.
Thanks, again for the account of the Alaska trip!

[Robby Ackerman]

Wilton

Thanks for your comment about reading the story about the Alaska trip in THE STAR. Frank Barrett was gracious enough to publish it. I'm glad I didn't spend most of the day trying to find a hot terminal when the switch is pulled out. I can benefit from your experience!

Cheers,

Robby

I read an article about 2 years ago on the benefits of daytime running lights. The NTSB gave them high marks for assisting drives to see a vehicle more easily. Anyway, I bought a 1983 300SD and I thought about trying to hook up the fog lamps as daytime running lights. I know, purists are cringing about now. So here is how you do it if you are interested.

The process started with the fuse box, which is under the hood on my model. I looked at the inside cover of the fuse box and saw that fuse #14 was a 25 amp, it was for the rear defroster and heated seats (which I don’t have) so it had amperage to spare. I tested the fuse with a voltmeter and found it was hot only when the ignition was fully on and was cold when the ignition was off, perfect. There are two recessed screws toward the front of the fuse rack, remove them and gently pull the fuse rack up. You can then locate the screw connection for fuse #14. I took some 12 gauge wire, crimped a connector to the end and removed the connection screw to #14 fuse and put the wire on it and screwed it down. I then ran the wire through the side of the box (snip one of the rubber grommet and put the wire through). I ran it through the firewall (again through a grommet) and brought the wire into the engine compartment proper. I put a toggle switch on a bracket near the firewall that wasn’t used for anything. I ran the wire to it and connected to one side.

Now, at the headlight assemblies there is a 4-prong plug that is the connection for the fog and headlights. After much testing I found that pin #1 was the hot for the fog lamp. I decided to hook up the drivers side first. I put a splice box on the wire and connected that to the toggle switch I had installed. With my fingers crossed I tested the “running lights”. To my surprise BOTH fog light came on! I tested everything with a voltmeter to make sure I had not created a voltage back flow or short. I also tested all my electric apparatuses in the car to make sure they worked. I even turned on the fog light with the switch inside the car (albeit they were already on) and all was fine. I check all the fuses in the fuse box and all were fine. I made sure that the wires were not over heating also. Everything was just fine.

So, I have been driving for a week and have not had any problems with the set up. The running lights give the car a newer look when it’s going down the road. I did it for safety reasons and I am glad I did. It makes me feel better when my wife and kids have that little bit of extra protection.

And for all the purist out there, all I have to do to return it to stock is flip the toggle switch under the hood and the whole set up is neutralized.

All of this is for what it’s worth………….

[Robby Ackerman]

Clancy

Thanks for your detailed description! And I never cring at any modifications owners make to their cars. Hey, even though I'm in my mid-fifties maybe my next modification will be to install underbody neon lights! At our next regional concours we should have an award for the most outrageously modified Benz.

Robby