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  #16  
Old 11-01-2010, 10:39 AM
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Quote:
Originally Posted by Renntag View Post
Scott,

Great right up. Thanks for the extra bit of info on the N7. I have lamp warning lights on from time to time and I have no lights out. I have dim headlights and have cleaned the grounds and chased wires. While my lights are still dim, I drive on High beam at night, clearly i have not resolved this issue. As a last resort, I did think of doing just what you have described.
Now that I am trying to install some Euro lamps I think I may perform this relay mod.

I would still like to get wiring diagrams for the lighting system on an '87 300TD.

Thanks in advance to anyone that can help.

Ha, same issue on my 87 300D, The low beams are so low you can hardly see driving with them. I turned on the fog lamps and drove like that. If I use the high beams I piss everyone off... My headlights are really worn, the plastic around the edges are crumbling, it's time to just get some replacements. I have been looking at some of the aftermarket jobs off ebay. anyone use any with success? ANYTHING has got to be better than what's in there right now.
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  #17  
Old 11-01-2010, 04:56 PM
92 300D 2.5L OBK #59
 
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I picked up some depo euro's $170 Delivered.
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  #18  
Old 11-10-2010, 06:19 PM
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Quote:
Originally Posted by scottmcphee View Post
I said I'd post a few pix of how to do quick surgery on your N7 bulb out indicator module. Turns out it takes a double frontal lobotomy to make N7 not pay attention to the headlights on the car. One nick for the low beams, the second nick for the high beams. I'll leave it to you to figure out which is which.

You can do this mod if for any reason you are getting dash lamp out indicator for headlights or highbeams, and they seem to be working fine for you. Maybe you can't figure out why, or simply don't want to figure out why, and it's just annoying because things are working just fine. Maybe your bulb wattage is off, or you upgraded to HIDs, or LED lights, or whatever... I did it because my "lamps" had been converted to relays, as noted in above post.

Here's how to do it.

Find and remove N7 module from the car, it's in the fuse box. Take it out and open it up.

Note the WHITE arrows I painted on the photo pointing to the plastic peg(s) that prevent wrong insertion. This will orient yourself as to which side of the unit you should be working on.

The PURPLE circles show what to cut on one circuit board.
You can cut that thin trace leaving both the encircled pads. Or you can do what I did, heat and lift those two diode leads from the board. Just left them hanging in air a bit off the board. (This way I can re-insert the leads in the future if I ever want to revert.)

Flip the unit over. Note again the WHITE arrows to re-orient yourself to correct side of the unit.

The BLUE circles show what is cut on the other board. Cut either that trace going between the two encircled pads, or lift the jumper wire out at one end.

Now pop it back together, and re-insert into the car.

Doing this mod leaves all other bulb indicator warnings intact.
So i just pulled the indicator module and the circuit board looks different. i have posted pictures below. can you help me diagnose what traces i have to cut? this came out of my 1995 E300D.

thanks







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  #19  
Old 11-10-2010, 07:32 PM
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1987 w124 300D
 
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Newer revision, but it looks like the same technology (ULN2455) now an obsolete part.

The philosophy of this circuit is that it is a comparator that funnels a bunch of outputs into a big "OR" circuit, such that any "true" condition that turns on the dash bulb out indicator lamp. I just found the headlamp inputs pins on the module followed them to the ULN part that measured them, and "snipped" the associated outputs (traces) from the ULN part. With these outputs no longer feeding the the big OR, they don't trip the dash light.

You need to get a pinout of the ICs on the board. It's actually hard to find, being obsolete and all.

Without having the part in my hand, I hazard not to guess at what to cut.

I have spare N7 module, I could mod and sell to you!
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  #20  
Old 11-10-2010, 09:20 PM
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could you show me where the headlight pins are? that way i could try and trace them. and how much would a modded N7 cost?

Thanks
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  #21  
Old 11-10-2010, 11:17 PM
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1987 w124 300D
 
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Quote:
Originally Posted by arcticathlon View Post
could you show me where the headlight pins are? that way i could try and trace them. and how much would a modded N7 cost?

Thanks
Headlight pins on this part can be found in the on-line service manual, the FSM. There are tons of links to it around here. I have downloaded a copy to my hard drive it's so useful so I don't have a link to the web version off hand.

PM me about the sales of stuff, or I'll PM you.
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  #22  
Old 11-15-2010, 09:11 PM
sjh sjh is offline
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Headlight Wiring Diagram

Greetings,

The entire wiring diagrams for w124 may be found here -

http://www.w124performance.com/service/w124CD1/Program/ETM/ETM.pdf

It's a big file (77 MB).

I've isolated the headlight wiring diagrams. There are two, 1986 to 1990 which is here -

http://thetwodocs.com/lights%2886-90%29.gif

and 1991+ which is here -

http://thetwodocs.com/lights%2886-90%29.gif

I did not upload them to PeachParts as their size limit results in an image that is hard to see.

Also the older schematic is very difficult to read so I have created a larger version that is more legible. It is here -

http://thetwodocs.com/lights%2886-90%29_detail.gif

I wish to entirely remove the low/high beam headlights from this circuit. Apparently I can remove 4 diodes as per this link -

W124 Headlamp Voltage

Or entirely bypass the relay as per this post -

Bulb Failure Warning Problem

---

I'd like a little advice as to which leads I should remove from the relay and tie together.

Thanks.
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  #23  
Old 11-18-2010, 11:10 AM
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1987 w124 300D
 
Join Date: Mar 2008
Location: Edmonton, Canada
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Quote:
Originally Posted by Dr_SJH View Post

I wish to entirely remove the low/high beam headlights from this circuit. Apparently I can remove 4 diodes as per this link -

W124 Headlamp Voltage

Or entirely bypass the relay as per this post -

Bulb Failure Warning Problem

---

I'd like a little advice as to which leads I should remove from the relay and tie together.

Thanks.
If you bypass N7 by shorting around it, I think your dash indicator will still come on. It will detect an absence of voltage.

And in post 2504982 those aren't 4 diodes, it is 2 diodes and 2 jumpers. OR you can nick the 2 encircled copper traces, one per side. But as people have noted, this is one version of the board and others exist so YMMV.
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  #24  
Old 11-29-2010, 06:07 PM
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1987 w124 300D
 
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Location: Edmonton, Canada
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I found the spec sheet for the chips used in this N7 module.
Attached Files
File Type: pdf ULN2455a lamp monitor.pdf (499.9 KB, 228 views)
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  #25  
Old 10-20-2014, 04:51 PM
300D-91's Avatar
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Location: Eastern PA
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Last week the BOW came on when I turned on the headlights. Very odd because the resistors I installed as part of an HID upgrade have been successfully fooling the BOW module since Jan 2013. Turns out that one of the resistors had given up the ghost. Although the resistors worked, they got very hot and that has always been a concern for me. Based on the posts from Scott McPhee earlier in this thread I was inspired to do an N7 mod. After opening my N7 it turned out to be the same version shown in arcticathlon's post . Using the ULN2455a product spec (Scott posted) I was able to reverse engineer that version of the N7 module and eliminate the BOW for both low & high beam .

To disable the BOW for the low beams (N7 - pins 2 & 4) I disconnected the diodes in the red box shown below.



To disable the BOW for the high beams (N7 - pins 1 & 3) I disconnected the diodes in the red boxes shown below.



WARNING: Before you go cutting or removing parts from your N7 based on this post - I suggest you check your cars wiring against the wiring diagram. The factory wiring diagram (below) shows low beam as being on N7 pins 1 & 3 and high beams on 2 & 4. Using a multi-meter I was able to confirm that on my car (91 300D) pins 1 & 3 are high beams and pins 2 & 4 low beams - reversed! In this case that wouldn't have been an issue because I disabled both low & high. However I don't know if Mercedes used the same pins for low & high on all models. Check and double check before modifying your N7....



Good Luck!
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Last edited by 300D-91; 10-25-2014 at 02:07 PM.
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  #26  
Old 08-03-2015, 05:13 PM
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Thank you scottmcphee and 300d-91 for your awesome pictures and details. I added HID when i replaced my headlights (buckets and all). Though they were supposed to be error free etc i threw a exterior bulb warning. My N7 was the variety 300d-91 showed the fix for. I can say that with some careful snipping, the warning bulb is off! You will need the smallest snips you can get to perform the work but all told it was a fifteen minute job. Thank you again for the super easy fix!

Last edited by k26ripley; 08-03-2015 at 08:35 PM.
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  #27  
Old 08-03-2015, 05:18 PM
300D-91's Avatar
Das German Diesel Mann
 
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Glad it was of help to you, best wishes.

Quote:
Originally Posted by k26ripley View Post
Thank you scottmcphee and 300d91 for your awesome pictures and details. I added HID when i replaced my headlights (buckets and all). Though they were supposed to be error free etc i threw a exterior bulb warning. My N7 was the variety 300d91 showed the fix for. I can say that with some careful snipping, the warning bulb is off! You will need the smallest snips you can get to perform the work but all told it was a fifteen minute job. Thank you again for the super easy fix!
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  #28  
Old 08-03-2015, 08:41 PM
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Sorry I left this out: Mine is a 1995 E300 D. Thanks again!
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  #29  
Old 10-11-2015, 01:19 AM
zu! zu! is offline
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Quote:
Originally Posted by scottmcphee View Post
3. upgrade voltage to the headlamp. This is what this original poster was asking about 3 years ago. There is too much voltage drop through the MB + side of the supply to bulb, more on that later. Here's how to minimize it: bring both plus and ground from the battery posts to the lamp area on minimum 14 AWG wires, 12 AWG is better, these beefy new wires must be fused at the battery side. I used 20AMP per wire for a good reason. Pro-tip: avoid having to run 4 wires by running a common rail of 2 wires that passes behind by each headlight. Rotate the second side of the car's connections to the rails so it's high beam shares the low beam rail of the other side of the car. Both wires are active for low, and and high - just the roles reverse. When you do this, one blown fuse means one side of the car remains working on low beam and the other side of the car on high beam - but you'll still have some light at all times. If you notice this failure pattern it's probably your fuse and not two filaments in different bulbs going at the same time. Beware, it is possible to hold the light stalk just so (as if doing flash to pass in slow motion) to get ALL FOUR beams ON at the same time. This is why I chose 20AMP fuses for the 2 wire idea. If you're antsy run 4 wires. Back to the program... cut the three wires going to each headlight lamp (3 wires for 9004 bulb), leaving enough length on the socket wires to remain useful. Repeat this for each side of the car: wire the car-side of the bulb supply with 2 relays, one relay coil for low beam, other relay coil for high beam, using car-side bulb ground for the relays only. Now when you operate headlights you'll only get relays clicks and no light until you connect your beefy + supply from the battery through the relay contacts to the bulb socket. One rail and a relay for low beam, the other rail and relay for high. Attach the bulb socket ground to your beefy ground wire. You can't get lower voltage drop than this for any headlight style assembly or bulb type!
OK, I know it's an really old thread, but Scott's solution above really intrigues me. I thought it would be an easy thing to do, so I took my headlights out already and even desoldered the plugs on the passenger side and connected relays to them (one for high, one for low and one for fog).

And right now, my relays click with no + power coming from battery, yay. About to hook up power, but then I reached the part about "rotating the second side...". I'm stumped. How would this work?

I searched some more and found another post by Scott that read:

Quote:
I brought out two heavy wires from the battery, separately fused, and passed both wires by each headlight cluster, buss style. On the left side of the car I tapped low beam relay to wire#1 and high beam from wire#2. On the right side of the car low beam on wire#2 and high beam from #1.
I drew it out, and to my simple mind, it didn't make sense. So in essence, he's saying hook up terminal 87 to Low Beam of left headlight AND high beam of right headlight. So...when I switch on my lights, I would get one high and one low beam? I can't seem to wrap my head around this.

I PM'd Scott and now realize that he's sold his Merc and may not be on the forum anymore. Can anyone else understand this? Help!
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  #30  
Old 10-11-2015, 03:19 PM
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Any ideas folks?


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