MB Tech - USA

Helpful information for 129 owners interested in upgrading the headlamps:

After upgrading to factory Xenons on a late model 129 chassis, you will notice that the high/low beam switch does not function like a factory Xenon vehicle.

The factory vehicle with Xenons always keeps the low beams powered up and turns the high beams on and off when the switch is activated. This is basically because Xenons do not do well being turned on and off rapidly, and some other reasons which don't matter at the moment.

The factory vehicle with halogens will toggle between the low beam lamp and the high beam lamp when switching.

The problem is when you bolt in those new factory Xenon headlamps into a Halogen vehicle, the xenons (low beam only) will shut down when switching to high beam. After some intense investigating, I found the fix and it's very simple.

Where the vehicles wiring harness connects to the combination switch (high/low beam - wiper - etc..), there is a loop wire on the vehicles harness side. (this is located under the dash on the drivers side) This loop wire supplies 12v to the low beams anytime the headlamp switch is in the "on" position. You remove the wire from the connector on the vehicles harness side and plug it into the wire that is taped back into that same harness.

In the long run, it makes sense. On the assembly line, depending on which lighting option the vehicle had, they only had to make a simple 1 pin harness connection change, no special control units or switches. Remove the wire from the connector and plug it into the voltage supply wire on the same harness.

I was lucky enough to have a 129 with Xenons parked next to me when I installed the factory Xenons in my 129 that came with halogens. It took some time to locate, because the factory wiring harness does not show this, so I hope this helped anyone with the same dilemma.

Good Luck!

kerrypacker

Based on your theory here, could I apply the same technique to facilitate daytime running lights? I brought my car up to Canada from Florida and the DOT requires a conversion for daytime running lights (DRL) At the moment, I am running a universal kit, which does not allow some functions (flash to pass)
Let me know if I can fiddle with that harness in order to get rid of that DRL kit.

MB Tech - USA

Hey kerrypacker,

The wire I'm referring to supplies a constant power supply anytime the headlamp switch is turned on, it's not connected to the ignition switch, so it would not work for daytime running lights, as I understand them, they need to be on anytime the ignition is turned on.

I’m not sure why the DRL kit you installed will not allow your high beams to flash when the switch is toggled.

If you could find a wire that has a constant 12v whenever the ignition is on, then you could connect it to the wire I'm talking about and this would give you DRL.

Hope that was helpful

kerrypacker

MB Tech. Response noted.
I have enquired around on the DRL issue at the MB dealer to find a simple fix.However, the technicians seem not to really know ( not really surprised at this)They recommended the aftermarket kit and installed it.

My question on the forum is: What, where, how, did MB do the fix for Canadian cars and U.S cars. Any suggestions? I want to get this aftermarket @#%#@ off my car.

kerrypacker

Just for folks wondering what the DRL fuss is about, here is the scoop.
The Canadian Ministry Of Transportation (similar to DOT) requires that all cars imported into the Canada from the U.S after 1990 requires daytime running lights (DRL), 8 MPH bumpers and instrument clusters showing speeds in kilometers.
When we brought our 320 back from Fla, the perfectly good bumpers had to be replaced at $2000 each. U.S cars only requires 5 mph bumpers. Replaced the instrument cluster and installed DRL. I am a stickler for OEM and could not do an original DRL conversion.
These and a few other crazy requirements made bringing my baby here a real pain in the .....

TheV12pwr

Why you made it so complicated?

sanyata

Hi, This is my first post as I just bought my first '98 SL500, Sport, Xenon, Pano Roof, Silver w/38k miles about two weeks ago.

Anyway, my xenons do not stay on when the brights are clicked on and they are from the factory. I've pulled the carpet part of the drivers side dash and the black plastic cover that is underneath. Is the plug you're talking about the one that is clipped into a bracket that has two or three other plugs clipped in also, and easily accessed, or the plug that is buried in the steering column?

I've printed out TheV12pwr's diagram but it still isn't clear to me what to do.

Any advise would be welcome...

Thanks,

Doug

sanyata

Two days later and I've got it all figured out. I found the extra wire taped back but ended up doing it with a jumper wire as per the diagram. Then I replace the high beams H1's with PIAA Extreme White H1's. Gotta say, "I LOVE IT!"

Gone is the yellow high beam hue and the white hue is a huge improvement. And no nano second lapse of light when going between high to low.

Now I'm thinkin' of replacing the driving/fog lights with the same PIAA's.



Doug

Pigzmickey

Can anyone translate for me, my German is poor.

Regards...

sanyata

Pigzmickey,

You don't really need to know German. The numbers for the pins are what's important. If you look at the diagram, the red line is a jumper wire that you use to connect pin #1 to pin #3 on the steering wheel side of the plug. My #1 wire was white with yellow strip and the #3 was a solid orange color wire. The plug was the second one from the right of the four plugs secured in a holder located behind the plastic that covers the underside of the dash above your feet. It was easy to indentify because it did have the extra unused wire taped back on itself, just like the first posting said.

I didn't want to splice anything so I used a solid core #14 copper wire bent in a "U" shape and forced it in the two pin slots. It was a very tight fit and I don't think its going anywhere and , as I said, I didn't cut or splice any wires.

Hope this helps!

Doug

Pigzmickey

Cheers Doug, is the an American layout or UK?

MB Tech - USA

Hello TheV12pwr,

The only problem with the jumper is that the low beams are only on when the light switch is turned on. A true DRL system turns the low beams on anytime the ignition is switched on. Hence the reason for the DRL kit. Your solution will not work for kerrypacker.

Complicated? Your solution works for converting to Xenon, true - I was just providing the factory way to convert as opposed to bridging wires which can then make future diagnosis of problems “complicated”.

To each his own….

sanyata

Mine is an American layout.

I did try using the extra wire but wasn't successful finding which wire to connect it to. And I was leery of just plugging in every wire and trying it until I found the right one. Electronics is not my strong suit! I doubt if the jumper wire will cause any diagnostic problems later but time will tell.

Doug

TheV12pwr

Hi MB Tech,
There is no need to get excited,I was just replying to your first post in the thread.
'complicated' is the word for most of the members reading your thread.
I am sorry if you feel offended in any way.

MB Tech - USA

Hey TheV12pwr,

No, not excited, sorry if it came off that way - I was hoping the "to each his own..." would soften the message. Just clarifying my point, and your right, it's difficult to explain wiring mods via text. I just like to find the factory fix if possible and thought I would share the results. More importantly, just letting MB folks know that it's possible - some have written me e-mails, to which I can explain more in detail or answer their specific questions to get it right.

Thanks for being civil, Later.

MB Tech - USA

Hey sanyata,

Glad to here you got it all worked out. I will have to try the PIAA bulbs, the color difference is annoying. (thanks for the tip)

My comment for diagnostic problems later comes from the fact that, from time to time, I get modified vehicles that have a problem, sometimes it's hard to tell what the customer was doing when you see extra jumpers - and sometimes the customers forget to tell me - so I guess it's a point of frustrations for me personally when working on older models.

Sometimes it gets even better, the vehicle is sold, then the modified part fails, so we replace it and now the vehicles doesn't work like it used to - that means I now have to spend more time (time is money) to find out why.

Long story short, I always try to at least provide the factory solution if I know it.

FYI - The wire you found taped back provides 12v constantly anytime the headlamp switch is turned to position 2. You plug that wire into the wire that goes to the low beams. (I don't know the color, and the color isn't always the same - so it's best to use a meter to check if your unsure)

Way too much to type – I can’t wait to try the bulbs!

sanyata

MB Tech,

The thing that confused me is that the extra wire has a male plug, unlike all the other wires coming from the same vehicle side of the harness, so it could not be plugged into wires on the steering side of the harness. I did check things with a meter and determined which wire was the low beam. I just figured I had to connect the 12v supply wire from the vehicle side to the low beam wire from the steering side, and they were both male plugs. Should I connect it to the same side low beam wire, thus the "loop" referance?

I agree, I would much rather have it done to MB specs than jerry rigged with a jumper wire.

You'll love the bulbs, just a tad too much $$$. But, I'm thinkin' of doing the driving/fog lights with the PIAA's also. <grin>

Doug

MB Tech - USA

Hey sanyata,

That's it. The vehicle side has all female plugs and one male plug that has the 12v on it. Just find which wire with the female plug on the vehicle side that feeds the low beams and plug the one male into it. The Loop.

It’s really ingenious of those Germans. Depending on which lighting package was installed, the wire harness configuration could be done on the assembly line by the installer, as opposed to having two different harnesses for the vehicle and then having the headache of tracking more part numbers, stocking more parts and costing more to produce.

sanyata

OK, I'm going to go back in and give it a try this weekend. I assume that means the low beam wire on the steering side becomes dormant, right?

Speaking of ingenious, the plugs with their locking mechanisms for the two halves, as well as holding the pins in, are pretty cool.

Thanks for the help....

Doug