A regular 30 ampere circuit breaker will do the job, the only thing is dismounting the head light switch and adding in the new wire (1.5MM IIRC) and mounting the breaker securely , you don't want it floating 'round loose under there .

A head light booster relay might be easier and would certainly give you brighter head lights even with the original # 6012 seal beams .

Look here :

https://www.google.com/search?q=headlight+booster+relay&tbm=isch&source=univ&sa=X&ved=2ahUKEwixgrS_gOToAhU0O30KHbQqCvAQsAR6BAgHEAE

The better kits with have fuses or circuit breakers .

I'm still hoping some one here will come up with a list of the circuit numbers and perhaps colors....

This used to be standard stuff when I had my shop long ago .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Well, I have 80W low beams and 110W high beams with H4 euro lenses that I have been running for several years now. The Euro pattern tosses the light down the road in a more focused beam so it does not annoy oncoming traffic. Anyway, I added 4 relays (1 for each low beam light and 1 for each high beam light) I also added 4 in line fuses (1 for each lamp) Yes, it may be overkill, but I only have the current draw to power the relays going thru the headlight switch, and with a fuse for each light, if one blows, I can still use the other lights (or the fogs in a pinch if all hell breaks loose).

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

No, this is certainly not any sort of overkill .

It's *exactly* what anyone running higher out put lamps should do .

I spent some time looking at the link I posted and most have fuses, I'd really think circuit breakers would be better and only a few dollars more if you do it at home .

God knows the junkyards are full of those cute little cube relays with mounting tabs, most are at least 30 ampere rated and all are continuous duty....

We used to have ...I forget the band name of street sweepers in our fleet, they used the HELLA brand relays every time the big bulky American made ones gave up on the 100 watt gutter lamps....

Geeze I'm getting old ~ I used to know all the brands and part #'s off the top of my head .

(they were crappy sweepers with hydro-static drives that jerked mercilessly) MOBIL made the very best sweepers ever until the idiot college boy whiz kids came in and ran the company bankrupt in about four years by bean counting & using vastly inferior materials)

I found a junked W123 nearby in case I can't find the old switch I had stashed, ,it's been rainy and damp here so I'm dragging my heels instead of taking the car apart and discovering burned wires behind the dashboard....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I went to the LKQ yard near me and found a nice 1985 W126 & harvested the switch & rubber dust boot out of it, jand polished all the wire terminal ends until they shone then installed it .

The old switch melted where the white / yellow trace headlight feed wire attaches, none of the wires showed any heat damage, whew .

I wanted to make the light in the middle of the knob come on with the fog lamps but I couldn't find the service notes for that, I remember someone posted that a while back .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

That light is for the rear fog lamp, Europe only.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

I know that, why I said I'd like to re purpose it for the front fogs lamps...

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Sure would be sweet if someone re-posts the details or pastes the link. Fingers crossed.

I'm hoping.....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Déjà vu

Step 9 in the folowing link.
How-to: Get the rear foglight(s) working on a US w123 (links to photos)

Additional info from the diagram for FSM job 54-305, terminal 31 is the ground for the rear fog lamp.
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Chassis/54-305.pdf

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

There ya go! Ask and ye shall receive! That's the great thing about this forum, always some one willing to help out.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Bravo.
And a heartfelt thank you!

I'm using my rear fog lamp bulbs as additional brake lamps, I only wanted to have the knob indicator lamp work on the front fog lamps....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I've done the brake light mod for 'Desert Rose' as well.
W116 Brake Light Mod


Run a ground wire to terminal 31 and you will get the desired result.
Remember, turn off your radio before you disconnect the negative battery cable.

Add a teminal screw with a small lock washer to terminal 31.
Run a ground wire from terminal 31 to the ground cluster behind the instrument panel.
For testing, I temporarily installed a spare haress wire to teminal 31, and connected it to the body of the parking brake release cable bracket to ground it.

I'll be using brown wire with ring terminals and heatshrink tubing for a factory look, when I make this mod permanent.

Attached Thumbnails

   

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Thanx ~ so all I needs do is add one brown wire to the #31 terminal and I'll be good to go ? .

Sounds great, I already sourced and installed the proper frosted bulb to the switch .

As you mentioned, I ty to always use the correct color wires .

I have spare correct screws & washers from the replacement switch .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Yes. you should be good to go.

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022