Front fogs on with parking lights DIY

[1980sdga]

It's always bugged me that the wiring in my car won't allow the fogs on with anything other than the lo-beams so I figured it was time to investigate.

After looking over the wiring diagram I discovered that the fogs are powered by the same circuit (Fuse 13) that provides power to the drivers side lo-beam.  After removing the screw that retains the fuse holder I flipped the holder and removed the fog light wire (white/green) from the fuse 13 location, crimped on a new connector and moved it to fuse 6 which powers the cigar lighter and rear window heater. I'm hoping that putting them on this circuit won't cause any problems...

Now I can run my fogs with the parking lights or hi-beams 

[koan]

Now I can run my fogs with the parking lights or hi-beams 

Makes no sense at all for driving in fog.

koan

[1980sdga]

Not for fog but it does allow me to control the lights independent of the lo beams.  I'm hoping they don't pull too many amps for the circuit. It's a 25 amp fuse.

[Hemersam]

  MB must have had a reason for designing the system that way---probably too many amps pulling the battery down. I think that's what the owner manual states (I think).
Hemersam

[gavin116]

The reason for having the fog lamps as low slung on the vehicle as possible, and only working in conjunction with the side lights is to enable the light to 'cut' through the fog to aid visibility.  If you have normal driving lights or worst still high beams on in fog, the light merely illuminates the fog, and all you see if a wall of white in front of you! 

I suspect that 1980sdga is not using these lights for fog, but more for deer spotting, in which case this setup may make sense.  Gives new meaning to 'throw a little light on the subject'.  I would however be weary of a meltdown leading to a fire in one of the harnesses!

[Type17]

The reason for having the fog lamps as low slung on the vehicle as possible, and only working in conjunction with the side lights is to enable the light to 'cut' through the fog to aid visibility.  If you have normal driving lights or worst still high beams on in fog, the light merely illuminates the fog, and all you see if a wall of white in front of you!

Indeed, fog doesn't hang below about 18 inches above the ground, so fog lights are designed to take advantage of this fact, by being mounted low down on the vehicle, shining a low, flat and wide beam up the road, to light up as much as possible without shining into the fog itself, avoiding the 'white-out' effect. This is why most cars are wired to allow the foglights to work with the sidelights, so the driver can avoid using the dips in heavy fog.

[KenM]

The reason for having the fog lamps as low slung on the vehicle as possible, and only working in conjunction with the side lights is to enable the light to 'cut' through the fog to aid visibility.  If you have normal driving lights or worst still high beams on in fog, the light merely illuminates the fog, and all you see if a wall of white in front of you!

Indeed, fog doesn't hang below about 18 inches above the ground, so fog lights are designed to take advantage of this fact, by being mounted low down on the vehicle, shining a low, flat and wide beam up the road, to light up as much as possible without shining into the fog itself, avoiding the 'white-out' effect. This is why most cars are wired to allow the foglights to work with the sidelights, so the driver can avoid using the dips in heavy fog.

I thought in addition to these points which are all correct, that the fog lights have different lenses that don't reflect the light back off the fog as happens with high beams but rather allow the driver to see through the fog much more. Is this not the reason why French cars have the yellow  lense inserts?

[TJ 450]

Yes, and the yellow light allows much improved visibility in fog due to the fact that reflection is minimised. It has the added benefit of higher contrast as well.

Low-pressure sodium street lighting can also be used for this purpose.

Standard high/low beam in fog effectively blinds you of course.

Plus, in some localities, it is illegal to use the fog lights for any other purpose than driving through actual fog.

Tim

[jbrasile]

Jon,

We are talking about the factory fitted fog lights under the bumper correct?

European 116's have their fogs built into the main headlights and you can turn them on while only using the "city lights" function and/or low beam, but once you hit the high beams they turn off. Basically what you have done is allow the fogs to be on at any position of the light switch, as it's been said high beams in fog will only make visibility worse, however in clear weather the ability to have fogs + high should give a great light pattern since the fogs spread the light to the sides of the road.

Tks,

Joe

[1980sdga]

From what I understand, there were US regulations that required round headlights so we got the 4 sealed beams    There was also a regulation that allowed no more than four lights to be on at one time, so we got the fogs wired to the lo beams.

Can't have more than 4 lights up front. You'll put your eyes out... Need big bumpers too...

This is with the light switch pulled out to the first position. (The second position does nothing  )

Low beams:




Hi beams:



The fog lights under the bumper are factory installed for the US market    I like to run my fogs and corner lights in the evening/ morning/ light rain  for visibility. I couldn't do that before.

The  fog lights are really nice Bosch units that focus the light in a narrow beam that covers the ground a good distance in front of the car and the entire width of the car plus they illuminate the ditches well.  The sealed beam headlights leave a lot to be desired though... Then there are our bumpers 

[Big_Richard]

The sealed beam headlights leave a lot to be desired though... Then there are our bumpers 

Please dont start picking on our "rest of world" version headlights and bumpers again, our already fragile self esteem cannot handle it 

[Casey]

Newer MB's allow more flexible fog light usage by default.  Fog lights + high beams is very helpful when driving way too fast down a country backroad trying to watch for ice patches in the wintertime...    And sometimes in fog or heavy snow, fog lights only is quite useful.

My '86 W124 allowed this.  The W123's vary, I think it depends on the year and maybe target market - neither the '80 or '82 allow it, but the euro '83 does.