I'm in the process of replacing my '95 E300D engine wiring harness with a new one. I'll post info on where I purchased the harness and other details in a separate post once I get the new harness in and confirm its correct fitment and operation. This is a newly manufactured harness, not NOS. I'll take some pictures of the old and new harnesses and post them, along with my comments along with contact information for the supplier.

Looking at the old harness now that it is largely free, I can see that while my wiring isn't as bad as some pictures I've seen with cracked and shedding wire coverings, mine was definitely beginning to go with some longitudinal cracks visible in some of the wires plugged into electrical components. Looking at some of the none-engine harness wiring, it does not appear to be in the same condition and what I can see of it still appears to be completely intact.

In removing the old harness, however, I've run up against the firewall, literally. The last bundle of wires to be removed disappears through a hole in the insulation at the center of the engine compartment and seems to run into the area behind the battery. How does one get through the firewall without shredding the insulation? It appears there is some kind of clip behind the insulation just above the hole for the harness, but I see no way of accessing it. If anyone has run this route before, I'd appreciate any guidance that could be offered for completing the removal of the old harness and installation of new. Thanks!


Regards,
Tom

Tom,

The harness does indeed go "through" the firewall, but it all comes apart. There are two rubber seals going entirely across the engine bay, one at the false firewall and one just behind it. Both pull off, and then you need to take apart the plastic shrouding under the monowiper and over the air intake for the HVAC. From foggy memory, there are a couple of phillips head screws hidden deep in the crack of the plastic air duct.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Max: Thanks for the info. It turned out to be an easier removal than I thought, though not simple. Lots of small stuff to wade through to get to the channel the harness is run through. Your tip about the small screws was right on. I missed them the first time. You actually only have to take off the one on the passenger's side to peel the drainage screen off to gain access to the wire.

It was an interesting, revelatory evening removing the harness in at least one respect. I had decided to change my wiring harness some time ago when I had swapped out my glow plugs and had the intake manifold and plenum removed and saw numerous breaks in the wiring insulation. In addition, the wires running into some of the plastic plugs were devoid of insulation and totally bare, particularly the two plugs under the intake plenum.

What I saw tonight did not change my mind about the lengthy effort to track down a replacement harness, as you can see from the attached pictures. However, I was astounded when I finally got down the last harness plug--the one behind the battery--and saw the part number: 124 440 4032, which is supposed to be the latter version of the harness that replaced the soy-based 124 440 3032. I had never bothered going that deep to check on the part number since I assumed from the condition it was the earlier version. Without tearing the tape off the entire harness to inspect its overall condition, it appears from this evidence that having the latter harness really shouldn't provide one with much confidence regarding its longevity. Perhaps the soy-based material that was said to have been used on the early harness is not the problem with the harness failure?

Doing a quick compare placing the new harness over the old shows it to conform size-wise, and all electrical connections, save those for the glow plugs, are identical. The harness was supplied with six injectors which are identical in every respect to the originals except that they take a different end connector since the original ones are NLA. This seems to make it possible for individuals who wish to attempt to rewire the harness themselves with an option. More details tomorrow.

Attached Thumbnails

         

Re the part number difference on the E300D engine harness. After some additional research last night, it appears that the defective harnesses may be determined by date of manufacture rather than the revised later part number, as I thought in my earlier email. My old harness has lost its date tag so I cannot tell date it came off the line.

The date tag is on your harness - and it shows a 1993 year, meaning its an original one from the factory. My car has a later one and is dated 2004, still in very good shape.

I have however rewired some E320 harnesses and E300 harnesses by reusing the old connector cases and lugs - the old MB harnesses are relatively easy to work on compared to new models. Its not a good idea to do this as your first harness rebuild project, if it is then get some supplies for marking and writing down whats what and take lots of pictures.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I am in the midst of this project. The main wiring harness and the glow plug harness.

What is the best method for extricating the harness and removing the hard plastic routing Shell to replace the innards?

Jeez, that hard plastic shell is tough all right. I guess it should be but it's a challenge.

This is a device used to cut the much softer outer oval shaped white plastic sheath on Romex home wiring. It's crude, probably this exact device is too crude for the sheaths in question. But the principle is nice. Those sheaths present some problems. They are generally a bit lumpy, with little hills and valleys along the way. A blade depth that would cut nicley through the sheath thickness w/o damaging the wire within would likely barely cut at all in spots. I imagine a more complex device with an adustable depth exacto knife blade mounted. Something that can be sharpened. But somehow I doubt such a thing is on the market and making your own can be a long project.

Sharpening the little nub of a blade on this thing could be dicey - soon you'd have no blade left. OTOH, it's cheap ($2.67), one could practice modifications on a few w/o much expense. Such as making the opening on the one end bigger, maybe even one sided so you could slip the thing over the sheath in odd spots.



https://tinyurl.com/y4rxr4rb

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1986 300SDL, 362K
1984 300D, 138K

Hair dryer to soften the sheathing and a curved linoleum knife to split the softened sheathing.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

That sounds good.

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1986 300SDL, 362K
1984 300D, 138K

Update: Got it done. I didn't end up breaking anything. For how BAD all the wiring was, the plastic routing shell was very flexible and I didn't break anything.

I think it goes to show you how BAD that insulation material really is.

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Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)