Sounds like an interesting upgrade.

One relay per light or one relay per pair?
Any circuit breakers or fuses in the setup?
Where do you mount the relays?

Thanks.

Jim

Jim,
I've used 1 30A ice cube relay per pair of lights, with each relay on it's own fuse. I chose bus push in fuses and standard spade terminal relays, to facilitate install and replacement. You can find pre-wired relay holders to have plug in relays.
You can of course choose MB hardware if you like, but it may take some work to get the relay and fuse holders.

I mounted on the fender well near the headlight buckets. The assembly is small and can fit nearly anywhere just find the easiest wiring route and leverage what is already there as much as possible.

What you are doing is simply shifting the bulk of the current load from the factory wiring and thru the switch to just to the relays and lights, the rest of the system doesn’t see more than 1A going thru it.

Also a good upgrade for power windows too

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

I'll give it a try. Thank you!

I did that exact same thing years ago. Definitely increased the light output.....haven't looked back since. In fact there are a few threads about that upgrade and how to do it here on the forums if you do a search.

__________________
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)

I can't find any how-to threads on the headlight relay upgrade. I was wondering if you cut the + power supply wire near the exterior plug on the light housing to divert the juice and rig it up to the relay, or if you snaked a couple of wires through an existing hole, or if you drilled a hole in the housing. I would prefer to use the existing connector inside the housing, but I don't know the route to get a wire into the housing. W123 1982 240D Thanks!

Hmm, I may be thinking of another forum I subscribe to. Anyway, the way I hooked it up was like this. I used one relay for both of the low beams and one relay for both of the high beams. I tapped into the + power wire from the headlight switch that goes to the lights to power each relay coil, and chassis ground for the ground lead on each relay coil. Then I ran power straight from the battery, through a fuse, to the input side of each relay, and hooked up each relay output to the respective wire coming from the headlight connector (either low beam or high beam). So in effect, when I turn on the headlight switch, the relay coils energize, closing the relay and routing power straight from the battery, through the fuse and through the relay, and on to the headlight.......Hope this helps.

__________________
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)

Echoing 87tdwagon's comments on relays, that really is the way to go. Headlight switches burn out from the full current going through them. Relays will shorten the current path to the bulbs, reducing voltage drop, making them brighter. Relays also remove the current load from the switch, eliminating the problem of overheating the switch.

For those that have installed these retrofit LED bulbs, it would be tremendously helpful if you could make a note to come back and follow up in this thread after 6 or 12 months of regular use. The online product reviews I believe are highly skewed, as many buyers give the product 5 stars immediately after installing it, but then fail to follow up their review when the bulbs burn out a few months later.

IME, when attempting to use high output LED's in a sealed enclosure, the heat becomes a significant challenge. Halogen bulbs tolerate high heat very well, however LED's really do not like to run hot. The sealed enclosures common in automotive applications trap the heat inside. The result is an LED bulb that burns out after only a few hundred hours - a far cry from the oft cited 50,000 hour LED lifespan. I'm beginning to suspect there is no good way to retrofit high output LED's into a sealed enclosure. I believe the OE applications are all designed with a heatsink integrated into the enclosure. Some folks leave the plastic covers off the rear of the lamps, in an effort to cool the LED's, but that of course voids the weatherproof nature of a sealed enclosure, so isn't a real solution.

__________________
Current fleet:
1998 E300 turbodiesel
2008 E320 bluetec - leaky oil cooler seals replaced
2012 S350 bluetec
2015 GL350 bluetec

Sold:
1996 Passat TDI
1997 E300 diesel

Jimmypete,
Look up "H4 (or H3) plug and play relay wiring harness". No cutting/splicing needed. I upgraded my headlights from sealed beams to Cibie with 100W hi, 55W low bulbs and a pre-made plug-and-play harness with ceramic sockets. Works great!

I also did the fog light mod where they can be turned on at any headlight switch position. I tried a couple of different yellow LED fog light bulbs from the auction site but did not like them compared to the stock bulbs. Very weak output even though the lumens advertised were high. Be cautious of chinesium junk.

That fog light mod sounds great. Is that a switch wiring mod?

Search this forum for directions on the fog light mod. I also did the rear fog light mod, its more involved than the front to get working. The results are a rear fog with the stock USA headlight switch, even has a bulb indicator that let's you know it's on!

O.K., I just searched " H4 (or H3) plug and play relay wiring harness " and " plug and play relay wiring harness " and got zero hits .

I know there's a detailed thread somewhere on this that includes diagrams and relay part #'s, it seems to me like the questioner here ( ? J.P. ? ) still isn't clear on how this works and so really needs the other thread so he can print out the diagrams and make this work .

J.P. : no, you DO NOT power the headlights from the headlight switch ~ you want to tap the headlight power from the battery or in the case of a W123, the glow plug relay , the idea being to :

A. shorten the current path from the battery

B. use the correct 1.5 MM diameter wire that will easily carry the headlight current .

The White (high beam) and Yellow (low beam) wires from the headlamp switch are only used to operate the relays, not carry the headlight current once you install the two relays .

For many having a diagram is the only way to fully grasp the idea .

Me, when I do this I use factory color coded wires so anyone in the future will instantly understand what's what and how to test / diagnose / repair it if ever something goes amiss .

I hope this helps, keep looking until you find the other thread.

Whenever I get off my duff and do this, I plan to use factory relays in the relay panel in the every top of the left inner fender under the hood ~ there are multiple open, unused places for factory relays to fit .

Amazon and The By of E. sell ready wired kits affordably if you're not up to making it all from scratch .

So far my Chinesium LED Fog lamps are working fine, I too had concern about how hot they get so I now drive with the fog lamps lit anytime I have the headlights on to speed along the testing .

I also have a pair of Chinese yellow halogen fog lamp bulbs in my gray market 300TD, so far so good, that's S.W.M.B.O.'s car so I don't drive it much and it almost never goes out at night .

__________________
-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

O.K., ;

Here's a quick Google link to the relays and how they work :

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

I spent some time looking for the old thread and cannot seem to find it .

Sorry .

__________________
-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

There are two types of fog lights, marked B and F3. Due to their design, the first ones are not suitable for installing LEDs. But in the second (marked F3) you can put diode lamps, their design involves working together with LED sources. You can find them in the car lights section of Amazon, for example. An even more reliable option from the point of view of the law is the purchase and installation of a new one with LED emitters instead of a standard fog lamp. Although I have not personally used this option, you can google it yourself if it's interesting for you.

I bought a pair of these back in 2017 for my Golf TDI. Swapped them over to my w124 when I got it a few years later. Still running strong. No noticeable drop in brightness. YMMV

https://www.amazon.com/Calais-Extremely-Bright-Golden-Plug-n-Play/dp/B01CTMT01G

__________________
1991 300D 2.5 "Rocinante"
2002 Golf TDI "Teen Spirit"
--------------------
1984 300D
1966 Mustang I6 3sp
1985 Mazda RX-7 GSLSE
1982 Toyota Supra
1977 Datsun 280z
1971 Datsun 240z

Way back in 2020 I bought the yellow LEDs off Amazon, they're still going strong, sorry I forgot to check back as requested .

__________________
-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