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  #1  
Old 09-21-2019, 10:10 PM
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Cool w124 300TDT ENGINE WIRING HARNESS

I have an 87 w124 wagon with a diesel engine that has a wiring harness that has become very brittle and causing various issues with blowing fuses to a/c going off and on. I saw on your website that part #124-540-25-06 mbz is available but for 1000.00 dollars. I've asked at several dealers and they told me it's no longer available, and I REALLY DONT WANT TO DISH OUT THE MONEY! Any suggestions on how or where to get supplies to use original guage wires with proper color code to rebuild the harness?????

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Old 09-23-2019, 03:21 PM
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Unless you've determined definitively that the replacement of the wiring harness is going to solve your issues, I would not spend the money. I too have some fairly brittle wiring, but I've found that the issues such as those you describe have other solutions. The brittle wiring is not that much of an issue if it is not disturbed and the insulation not broken. For $1000 I would be taking a look at other things.
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DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV
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Old 09-24-2019, 12:04 AM
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These are pretty straightforward in terms of repair, main thing is to get correct gauge wire to each part - this can vary greatly from glow plugs, to oil sender.

Once you have it removed from the black plastic box section it's not too bad.
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1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)
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Old 09-24-2019, 10:37 AM
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I don't believe there is much you can do here in the US to match up the colors of the wires.
You could get some best quality numbering sleeves to put on the wires and create a numbered index of what wire goes wear and what the original color was and keep a copy in the glove compartment, Computer, Memory Stick and so on just so you have enough copies that all will not suddenly get lost of destroyed.

Also Mercedes connectors are usually numbered for further identification.
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84 300D, 82 Volvo 244Gl Diesel
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Old 09-24-2019, 10:47 AM
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Note that on the internet there is watts/amps guides to what size wire to use and you can get some idea of that from the Fuse in the circuit.

You also might look on UK eBay.
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84 300D, 82 Volvo 244Gl Diesel
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Old 09-24-2019, 10:53 AM
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Just an odd question. Does anyone know of any electronic supply shops were you can go and leave an order for say blue with yellow strip wire and they will sell it by the foot or yard? And, do the same with other colors of wires?

I am thinking there must be in some large cities but I have always made due with what ever the Auto Parts or Hardware Store has.

Some of our members have mentioned that Marine Wire has superior insulation an finer wires in the core of wires. Perhaps a marine supply shops would have wire that you could cut to length you want.
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Old 09-24-2019, 10:54 AM
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Quote:
Originally Posted by Diesel911 View Post
Note that on the internet there is watts/amps guides to what size wire to use and you can get some idea of that from the Fuse in the circuit.

You also might look on UK eBay.
Yup, you can also measure the wire itself using micrometer, that said from memory there's only three or possibly four variants.

A good soldering iron is essential to remove existing wires from plugs, these can be reused afterwards.
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1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)
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Old 09-24-2019, 11:13 AM
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The FSM also shows the wire size in mm on all the electrical drawings. Most wiring is going to be .75, 1.0, or 1.5mm There are online charts that will convert the mm cross section to AWG for purchasing replacement wiring.
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Old 09-24-2019, 04:08 PM
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Quote:
Originally Posted by Diseasel300 View Post
The FSM also shows the wire size in mm on all the electrical drawings.

YES


here's the link to the 300TDT and other w124 wiring diagram:


http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/ETM/ETM.pdf
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Old 09-24-2019, 06:01 PM
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The 87 w124 ecu wiring harness has maybe 15 wires. I had several that I modified for simplicity which now have about 8 wires. Both harnesses did not have any wires which could cause any issues due to age, heat etc. The plastic cases the wires sit inside howerer were extremely fragile. I could source a 602 harness for cheap used but I really don't know what if any differences exist.
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01 e320
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  #11  
Old 09-24-2019, 08:21 PM
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There are some very good comments here. And in particular, I've found the wiring diagram to be helpful. Just one other comment on voltage. If it is not high enough, there will be trouble. My 87 would start and run just fine with a small old battery the previous owner had stuck in it to sell, but there were gremlins. When I replaced the battery with one properly sized, stuff worked. The sunroof worked suddenly and the abs light went off. Couple of other things got better too.

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DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV
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