Hi All,

While there has been a lot posted about rear fog lights, I have yet to see anything about the actual connection to the switch. Hence, my question: Has anyone added a rear fog light to their W126 (86+), and if so, how?

Just to make sure we're on the same page, I'll review what I _do_ know.

• The rear fog light is a P21W bulb behind a red reflector, located on the driver's side only, that goes on when the headlight switch is pulled out to the second stop. This provides better visibility for drivers behind you.
  
• DOT/SAE regulations first permitted them in the US in 1990. Most Mercedes models sold in the US have since had them.
  
• AFAIK, the W126 line in the US never had this feature, at least not for 1990-91. The Service Manual shows no revision for this setup, even though they have about 20 different revisions for heated seats.
  
• While there is a six pole connector for the W126 tail lights, all are spoken for. They are, in no particular order:
  1. Ground
  2. Brake Lights
  3. Backup Lights
  4. Turn Signal Indicator
  5. License Plate lamp
  6. Side running light (P10W). I assume this is the connection that would have been used for the rear fogs, especially since ECE regulations didn't require the side running light. The W124s don't have the silly connector for the license plate lamps since they are attached to the boot lid, which allowed the 1990+ models to have the rear fogs without any siginificant change.

I see several options. 1) Get the European tail lights and convert the wiring for the running lights to the one fog light. 2) Run an additional wire from the switch to the fog light. Adding the wiring in the currently empty socket is no problem. 3.) Retain the sidemarker light by combining with the license plate lamps - after all, they are supposed to go on at the same times.

Do any of you have any input as to which of these would work best, or if there is something else I should consider? I'm favoring solution 2), but I'm concerned it will have a very slapass appearance with the extra wire. At least it keeps me DOT legal, and I don't have to worry about modifying or disabling the "light out" relay (which is why the license plate and rear running lamps are on separate circuits, even though they go on at the same time). I assume for solution 1) that the resistance of 1 P21W fog light bulb is similar to the two P10W running light bulbs, so there would need to be no modification for the "light out" relay.

My other question is about how to actually wire the switch. The one in my car is a replacement and interestingly has the two stops, plus the ability to turn on the fog lights w/o the headlights. However, I couldn't determine whether the switch had any wiring for NS, which is the fog tail lamp output. Would that still require the purchase of another switch?

Lastly, if I do need to purchase another switch, does the one listed for the W124s and later W126s at Phil's shop have the necessary connections? My switch has the _appearance_ of that functionality, but not necessarily the functionality itself. I don't want to spend $50+ for what I already have.

Thank you for bearing with me on the long question and for any input you can give me.

__________________
Casey Cooper
"From a long line of Mercedes ownership"

'86 300SDL 250K miles (Gone, but not forgotten); best diesel I have ever driven, too bad about the Achilles heel.

'81 240D 370K miles (Sold to my brother after 9 years and 150K miles of reliable driving!)

[Five other Mercedes in family clipped for less length.]