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………….
1983 300SD Turbo
My first MB!