W124 Wiring Loom - have you had problems

[Bill_33]

Has any E280 or E320 W124 owner have a vehicle that has NOT had the wiring loom replaced.

I have just bought a E280 and obviously it is one of the first thing that I need to check once my son gives it back to me.

I bought it knowing the problem so it is not something that I am not prepared for.

Is the engine bay loom the only one that needs to be replaced, (if faulty) or is it the lot

Is the MBZ price for the engine bay loom about £500 or is this the price for a full loom

Cheers

 

[fnkhan68]

How do you know the loom needs replacing? What are the symptoms? I wouldnt bother if the car is running fine with no problems.
I have a prefacelift 93 320e with the M104 engine still on the original loom, all electrics work fine, no surges of the engine upon idle.
Just for the record it is the engine bay loom which often requires changing, about £500 from main dealers.

 

[andy_k]

last year the engine bay wiring loom was priced at £582 plus vat.

I got us an offer of a 'club discount' with our local dealer to supply them at £580 inclusive of VAT. I don't know if they'll still match that price as the parts manager has moved to another dealer (I can still contact him though)

Let me know if you need to get hold of one and I'll give him a ring

 

[andy_k]

How do you know the loom needs replacing?

just slide back a bit of the outer casing on any of the plugs/connectors at the front of the engine - if the wiring inside crumbles then you'll know the loom is knackered.

Unless it's been replaced (many already have been), most of them will be pretty much knackered and the problem will probably manifest itself when you come to change the spark plugs

 

[Bill_33]

How do you know the loom needs replacing? What are the symptoms? I wouldnt bother if the car is running fine with no problems.
I have a prefacelift 93 320e with the M104 engine still on the original loom, all electrics work fine, no surges of the engine upon idle.
Just for the record it is the engine bay loom which often requires changing, about £500 from main dealers.

I have no symptoms, (apart from a mid life crisis according to my wife for buying a 14 year old car!!)

I would rather not wait until it needs changing, the cost effective solution would be to change it if it shows any signs of deterioration

I did not say that I needed a new loom. all I wanted to gauge was how many people did not have a problem as the wiring loom problems seems to be a hot topic on the Forum which I am new to.

All I said was that it should be one of the first things that I need to check and that this was a factor that I took into account when I bought the car.

I hope that it is OK but I will not know until I check

 

[Ade B]

The problem I find with preventative maintenance is it can be expensive...

I'm now of the mindset that if it is working leave it alone until it breaks, keeping some cash aside to deal with the inevitable.

Having said that, I think a damaged loom can cause other problems so if you establish it is in need of replacement and intend on keeping the car, its a worth while expense.

Ade

 

[coupe deville]

I have an early facelift and as far as I know it has the original loom which looks ok, no crumbling or electrical maladies

 

[Druk]

There are never any outward symptoms. The first sign of trouble (and it's usually terminal) is after the spark plugs have been changed which requires the loom going to the coil packs to be bent back. When things are reconnected and the key is turned is when the ECU is fried. A loom that is completely gone will show signs of deterioration at the extreme ends at the plugs as per post #4 but it can be 'gone' only at the neck where it passes through to the coils and you would never know unless by slitting the cloth wrapping and having a look.
Colours are..............Black (hiding) no1 coil trigger. Black/white no2 coil trigger. Black/yellow no3 coil trigger.
Large pink/red.. +VE ignition feed to coils which goes live the second the key is turned.

 

[Dave Lewis]

I think this is one case where preventative maintenance can pay - when the loom does short, it can also take out other expensive items such as coils and the ECU. Since it's a definite, proven problem, it would make sense to replace it sooner rather than later.

 

[kth286]

agree with Dave Lewis if you have no history with car and cannot see from the loom label a date of some kind. Bulkhead end of loom.

Make sure you get the correct loom for your car and the options the car has - be very familiar with the options and give the full VIN to the Merc parts person.

 

[fnkhan68]

That was my point, most of these have cars have had the loom changed already so if its not broke why fix it? Best way is to closely inspect the loom and take measures accordingly. The M104 engines have a tendancy to go through at least one water pump so if the water pump is knacked the engine would be running at a much higher temperature than usual, therefore accelerating the disintegrating of the loom plus upon changes of spark plugs.
So was it a specific year for these disintegrating looms or is this problem generic for 2.8 and 3.2 M104 engines, the reason I ask is the mechanic who services my car pointed out that my car did not suffer from this problem due to it being a pre facelift model however I checked the loom for my own satisfaction as I have always assumed its engine based and not year of model.

 

[Druk]

So was it a specific year for these disintegrating looms or is this problem generic for 2.8 and 3.2 M104 engines, the reason I ask is the mechanic who services my car pointed out that my car did not suffer from this problem due to it being a pre facelift model however I checked the loom for my own satisfaction as I have always assumed its engine based and not year of model.

Mine was late 93 pre-facelift 320 and the loom was shot from end to end. Interestingly I'm in discussion on another forum with a guy who has a W124 220 cab and the loom is crumbling on that. Duff loom in a 220 is a new one on me and I've been at four 320 looms. Here's another place to test....cut carefully into the soft rubber sheath just before the maff plug (there are four wires in there and the sheath isn't molded to them). This pic with the maff plug cut open for repair but you can see the bad wiring.

 

[grober]

Since the problem is almost certainly accelerated by heat it occurs first in the 6 cylinder cars due to greater under-bonnet heat. How far the degradation has gone really depends on mileage and the running history of the car and how well its cooling system has been maintained. Lots of slow city driving on hot summer days with dodgy fans would stress the wiring insulation more and cause the insulation to fail faster.

 

[Druk]

Graeme.

It would seem logical to presume that this is a mileage/heat/time equation except that I've had a loom sent to me for dissection which came from a quality Indie maintained low mileage 320SL R129. Said Indie had stressed to it's owner the integrity of the loom, nonetheless it had been changed and upon close examination was found to be shot.

 

[grober]

As I understand it the history of this was that the insulation was designed to "biodegrade" in landfill sites as part of a Mercedes "environmental initiative" Unfortunately they got their sums wrong and it would appear it began to biodegrade in the cars. I think the wiring to build the looms was supplied by LUCAS industries.

I certainly feel that the modern practice of enclosing engine wiring looms under engine cladding, while making things look neat, does not help the temperature environment they are subjected to!

 

[Niks]

I have a E280 95' and so far its going really well but after reading the above, seems like a cause for concern!

 

[andy_k]

sadly, this problem doesn't only affect the engine bay loom (although this is the most common 'fix') but all the wiring on the car.

There are more wires under the bonnet which can fail - those going to the throttle actuator are also worth looking at if you have any running problems

 

[compress ignite]

Enclosure of Wires

In Conduits,Conceals,Etc. effectively DeRates the Amperage Carrying ability of the cable.(Due to the Heat Increase Potential)

(The Best Reference source I've found for Electrical Matters Is:
"Boat Owner's Mechanical and Electrical Manual" Second Edition
by Nigel Calder)

Grober,
'Were you stating as fact the wiring harnesses
(With built in self degradation before you've even purchased it)
were produced by Lucas Electric ,under contract, for Mercedes?

 

[grober]

In Conduits,Conceals,Etc. effectively DeRates the Amperage Carrying ability of the cable.(Due to the Heat Increase Potential)

(The Best Reference source I've found for Electrical Matters Is:
"Boat Owner's Mechanical and Electrical Manual" Second Edition
by Nigel Calder)

Grober,
'Were you stating as fact the wiring harnesses
(With built in self degradation before you've even purchased it)
were produced by Lucas Electric ,under contract, for Mercedes?

I can't swear to that to be honest but there's something in the back of my mind about it I read somewhere. I know some Volvos in the 80's were similarly effected. quote:-

Volvo 240s and 740s from 1980 through 1987. The insulation turns brittle and then cracks and flakes off, leaving bare wires. Volvo eventually started selling replacement harnesses that had a different insulation formulation, and those seem to hold up fine. In fact a lot of people replace their harnesses with ones from junked cars that had previously had their harnesses replaced with the updated ones. They're not too hard to come by for most years. Replacement is a chore, though, because we're talking about the ENTIRE engine harness, from the firewall connector forward.

 

[fenns]

There are never any outward symptoms. The first sign of trouble (and it's usually terminal) is after the spark plugs have been changed which requires the loom going to the coil packs to be bent back. When things are reconnected and the key is turned is when the ECU is fried. A loom that is completely gone will show signs of deterioration at the extreme ends at the plugs as per post #4 but it can be 'gone' only at the neck where it passes through to the coils and you would never know unless by slitting the cloth wrapping and having a look.
Colours are..............Black (hiding) no1 coil trigger. Black/white no2 coil trigger. Black/yellow no3 coil trigger.
Large pink/red.. +VE ignition feed to coils which goes live the second the key is turned.

Druk - thanks for posting this picture as now I have some idea of what a shot W124 wiring loom looks like! Fascinating - I didn't realise that the insulating material literaly splits apart as if someone has taken a Stanley knife to it

My recently acquired 1994 aW124 E320 with 64,500m seems fine at present but it appears that this deterioration is inevitable. I'm concerned about the resultant damage to coils and ECU when the looms goes so could you provide a summary of possible symptoms? I'm sure all W124 owners would be grateful - I know I would :bannana: