Soybean / Biodegradable engine wire harness on 91 - 94 models?

[MafiaDON]

Hey comrades..

I know that the very fist batch of W140 models that were built from 1991 - 1994 had a manufacturing flaw of the infamous "Biodegradable engine wire harness"

Due to high heat in the engine bay and age, the insulation on the wires dries up and crumbles off, leaving there wires bare to short-circuit with the other wires running parallel.

Most common is that the main, upper engine wire harness is the one which inevitably fails. It causes all kinds of major problems when failed.

MY QUESTION IS:

Are all the wires in car insulated with the same form of biodegradable insulation?

Are there any other wire harnesses that also fail due to this manufacturing flaw? Eg: Lower engine harness, electric mirror wires, interior electrics, etc?

[pcmaher]

Yes, there have been many failures of other harnesses in the car. But as you point out, the ones closest to extreme heat are the ones that tend to go.

[nubyOz]

Originally Posted by MafiaDON

Hey comrades..

I know that the very fist batch of W140 models that were built from 1991 - 1994 had a manufacturing flaw of the infamous "Biodegradable engine wire harness"

Due to high heat in the engine bay and age, the insulation on the wires dries up and crumbles off, leaving there wires bare to short-circuit with the other wires running parallel.

Most common is that the main, upper engine wire harness is the one which inevitably fails. It causes all kinds of major problems when failed.

MY QUESTION IS:

Are all the wires in car insulated with the same form of biodegradable insulation?

Are there any other wire harnesses that also fail due to this manufacturing flaw? Eg: Lower engine harness, electric mirror wires, interior electrics, etc?

Also not to forget:
- ETA (Electronic Throttle Actuator
- Side mirrors (wires move a lot, break, cause shorts and smoke)

Cheers

[Jayare]

The soy beans showed up on every Mercedes product built from 1993 - mid 1997. Upper/lower harness and ETA.

Jayare

[CDS32]

93 300SD Already replaced main engine wiring harness. Glow plug harness on order. Now the aux fans don't shut off after the key is turned off and will kill the battery. Seems like the electrical gremlins might get the best of me!!!!!

[Sinned420]

As others have said, its mainly the heat that kills the insulators. I have found that the wiring throughout the car has been great, but my fuel injection one I can see the crumbling off at the plugs. I already ordered a new harness which is coming in today (although I have no issues with the engine performance, preventative maintenance). I don't think the wiring from the mirrors die due to constant moving in and out. If that is the case, your whole door harness will suffer the same issues because that is constantly being opened and closed.

[Stryker-1999 S600]

For the W140, 1996 was the model year the switch from soybean insulation was made. 1995's and earlier had it, 1996 and later have the conventional wiring insulation.

Since MB spec'd out the production of the engine harness (upper as some some call it) and the body harness (lower), those were the ones with the soybean coating. The harnesses plug into components made by others (Bosch, etc) and those components did NOT have the soybean wires, so they are fine ONCE YOU REPLACE THE HARNESSES. Recent discussion on later models having wiring issues with the side mirrors I can't confirm as I have not seen evidence of that, but that may be an issue with some cars.

The electrical gremlins are a direct result of either NOT replacing the harnesses that are failing at this point, or worse: A PO tried 'fixing' the failing wiring harness by extensive use of electrical tape or some other 'home-made' concoction that got the car to the point he sold it to YOU.

At this point, 16-years into production for the latest models, it is safe to say that ALL soybean-based wiring harnesses either have been replaced or are in dire need to be replaced.

[MafiaDON]

thanks for all the feedback guys

Yes I also saw the side mirror insulation problem on my S500 while I was attempting to repair the mirrors. (Still waiting for parts from W210 mirrors.) There was even slight evidence or burning caused by the wires. but I insulated them properly. Will consider replacing them at a later stage.

I am also going to be looking at some engine wire harnesses for my S320, because the one that is fitted on right now crumbles even from just looking at it lol.. If I find a good condition one I will buy it on the spot

What I found interesting is that the wire harness on my 1995 S500 seems like it is made with proper wire insulation, not the soybean one. Maybe it was replaced if the change only happened in 1996?

Or did the change happen a little bit earlier? When is the exact date that Mercedes decided to use proper wire insulation on their engine wire harnesses?

[ramblinche81]

Originally Posted by MafiaDON

thanks for all the feedback guys

I am also going to be looking at some engine wire harnesses for my S320, because the one that is fitted on right now crumbles even from just looking at it lol.. If I find a good condition one I will buy it on the spot

If I had known last week, I could have pulled one from an S320 in Nashville, salvage yard that was in excellent condition. I go back in about six weeks if you can wait and the car is still there. Yard Cost is $15. I will sell to you for $40 plus shipping if you are interested...total should be under $75 US

Would it make sense for us to set up a parts swap want/need thread ?

[Stryker-1999 S600]

The wiring harnesses started to go bad within 3 or 4 years after production, so it's possible MafiaDon bought his car and it already had the switch. Replacement harnesses, like replacement evaporators, are much more long-lived than the originals because they were re-engineered to last, basically the life of the car.