I'm installing a daytime running lights kit, but I need to know if this car has positive, negative or double-negative switching. Anyone know? I also need to know if the lights are 2 wire or 3 wire. I guess I can figure that out just by looking, yes? THANKS!!!

ON that car the headlight bulb is always grounded. The headlight switch sends power to the "combi" switch & then to the fuse(s) & then directly to the headlight.

I guess that means positive switching??? No relays OR computer involved on that car.

Guess you could wire a lower voltage signal to the correct fuse to accomplish that task.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I used a module from a company in Canada to accomplish daytime running lights. It pulls power from the battery and uses a wire that senses ignition wire (spark plug) power for a trigger. Hence, engine has spark, module lets power flow to the headlights. It also has a voltage reducer built in becasue it supplies only about 50% of the voltage and the headlamps are not as bright when working in day time run mode. the power flow is stopped when it senses normal power supplied to the headlamps from the switch and the headlamps go on to normal brightness. Very slick. Inexpensive too, about $30 and 30 minutes to install. I also wired the power suppy to the module thru an extra hazard light witch that i had from an older MB ( no text or lettering on it) and I snappe dit in to the old location of the radio speaker fader switch in the gear shift console as a positive on off switch so if i dont want the daytime light to come on, I can turn them off. Because at night even if the lamp switch is on the off position, the day time light will come on, they are not light level controlled, they are engine on or off controlled. it all worked out very slick and it looks factory. I made a transparent background, white lettering overlay for the switch to label it as "DRL off" in the off postion and it all looks very OEM. I like it. AND, I got rid of the crazy factory speaker fader switch that I didnt need any longer!

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red

I'm in the process of upgrading the electrical in my SDL, and I have headlight/fog light relays on the list. The cool thing about relays is that you can add additional functionality, such as DRLs. I did some extensive research, so I'm glad I have a place to share what I found for installing DRLs.

OEM DRL Install ("O Canada")
The FSM has a detailed procedure for how to retrofit the DRL module for Canadian vehicles, which has the mandatory DRL requirement. While this keeps everything "factory", it appears to be a complicated install, and the module is $99 through Phil. Said module is pictured below and is located at:


http://catalog.worldpac.com/mercedesshop/...Daytime+Light+Relay

Note it references a '91 300E, but the part is the same for all W124s, W126s, and W201s. The procedure looks rather involved and rather than me explaining it, I'll defer to job 82-0071 from the W126 FSM. Unfortunately, I cannot upload the PDF as it is too large for the forum. If you're interested, PM me and I'll email it.

Aftermarket
There is a myriad of products available in the aftermarket, a la JC Whitney. The funny part I noticed is that there are more products for _disabling_ the DRLs than there are for actually installing them. The Canadian product crhenkel mentions sounds cool, but would likely not work with diesels, which notably lack spark.

Relays
My favorite - cheap, simple, but maybe not so elegant, which is to use the fog lamps. This has a similar appearance to more modern vehicles, some of which also use the fog lamps. Basically, I will take advantage of the fact the five-pole, standard relays have two outputs: 87a (when open - i.e. the controlling switch is off) and 87 (when the switch is open). IOW, when the relay is in it's natural non-activated state, there is a direct connection between the power terminal (30) and output terminal 87a. When the relay is activated, there is a direct connection between Terminal 30 and Terminal 87.

Basically, it's three relays in series. Relay One takes the _fused_ input from the battery (30) and the input from the fog lamp switch. When the fog switch is on, the relay is activated and the power goes to the fog lamps (Terminal 87), no surprises. When the fog switch is off, power is routed to 87a, which then is routed to Terminal 30 of Relay Two.

Relay 2 is what activates the DRLs. The switching mechanism here is a wire run from Circuit 15 (Hot in Run or Start) to Terminal 85. Even though standard DRLs utilize a sensor for forward motion, I'm confident having the lights on when the engine is running should be sufficient. When the key is in Start or Run, the relay is activated and switches power to 87, and the lights (and only the fog lights) are turned on. Nothing is attached to Terminal 87a, so when the relay is not activated, the light does not go on.

While the fog lights at full intensity (assuming 55W bulbs) fall within the candela requirements for DRLs, it is possible to get a relay the decreases the voltage, say to 10 volts to dim the lights. Or a simple resistor in line would do the trick. Kinda funny using relays to _dim_ lights, though.

Now the only problem is, what if one doesn't want fog lights on when the headlights are on? Simple. Relay Three accepts the (power) output cable from 87 of Relay Two at its Terminal 30. A cable is run from the power cable for the headlights (after the switch, relays). The only output is the cable from Terminal 87a to the fog lights. When the headlights are off, the relay is not energized and power goes to the fog lights. When the relay is energized (headlights on), Terminal 87 (with nothing attached) is activated - no power to the fog lights.

The only issue in using relays is that the Lamp Failure Module will register the lamps being burned out since the relay effectively reduces the resistance to nil. I happen to like the module for registering burned out lights that are not obvious, such as brake lights, running lights, &c. It would have been nice in my 240D when I was pulled over for having a burned out brake light, which unfortunately led to a $500 fixit ticket for not having DOT compliant headlights. How the officer noticed the E-Code lights were non-compliant still shocks me - as well as the $500 fine (you think I'd downgrade to the DOT sealed beam crap?)

I digress. AFAIK, removing the inputs and outputs for the relayed lights from the module should take care of the issue. If not, I'm also aware some of the paths on the circuit board can be broken, though I don't have specifics on that.

If all goes well, I'll be doing a write-up of my (mis)adventures, complete with diagrams. One other thing I'll mention here is setting up the headlights to go on when the windshield wipers are turned on, as that is now the law in California. BTW, original configuration is there are no relays on the lights and all power goes through the switch and turn signal stalk.

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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.]