W124 do I need to change the wiring loom?

[jazzdude]

On the whole, the wiring loom in the engine bay, although original, seems in surprisingly good condition. It is solid around the ECU connector, around the engine bay, and it seems that a new portion has been spliced in at some point in the past, across the cylinder head to all the HT leads etc.

I have an issue though with the two wires that go to the temperature switch just above the thermostat. The aux fans have just started staying on all the time and this started just after I had the A/c gas topped up, so obviously, the area had been disturbed with the refrigerant hoses.

So it seems somewhere along those wires there is a short as when I take them off the switch and touch them together the fans stop. Having just spent a whole lot on suspension refreshing and new tyres, my budget is dry at the moment with regards to starting a new big expense.

So my question is, can this section of the loom be changed for now or do I have no option but to change the whole loom. I have no misfiring or other issues with the car although since the fans have started staying on, the idling is slightly rougher when the car is in traffic.

 

[BlackC55]

What engine is it?

 

[Merc Owner 2B]

So it seems somewhere along those wires there is a short as when I take them off the switch and touch them together the fans stop.

From what you are describing the switch is faulty i.e. open circuit all the time. If the wires were shorted touching them together would have no effect. I presume that when up to temp the switch makes a pair of contacts and turns the fan off. Yours is staying open.

 

[jazzdude]

It is a 320.

I will check again but what can I do otherwise to test that it is not the wiring. The fans are on nearly all the time now but switch off momentarily at times, then come straight on again.

 

[krimat2005]

you said that problem occured after A/C top up, they might have put wrong amount in, who has done it? Try turning A/C off (EC button illuminating).

 

[WDB124066]

Sorry to hear this, hopefully you will get through all the little issues and settle into a sound well sorted car. I think we all go through this with the older cars - certainly mine gets a birthday on what seems like a monthly basis at the moment - but I love driving it when it's sortred..

I had a feeling in the back of my mind the fans were also operated according to AC coolant pressure and AC coolant temperature, have I got this right?

Maybe the pressure or temp is so high now that they stay on all the time...??
Maybe a sensor needs replacing now that it has a full charge of gas...??

Check out the attachment....

Let me know if you need a decent contact for parts at decent prices.

 

[Vlad]

If the wires to the top of the temp switch are showing signs of cracking/flaking insulation then you can be pretty sure that the rest, especially under the spark plug covers will be shot to pieces, albeit that yours appears to have ben repaired. The problem is that there are likely to be other areas of the loom that are also flaking apart.

Take a razor blade and cut through the outer insulation on another part of the existing loom and assess the condition...if its a flaky mess, you're living on borrowed time

If you just ignore it, you risk the loom shorting out which can have the expensive knock on effect of blowing the coil packs and ECU etc etc.

 

[Druk]

If the wires to the top of the temp switch are showing signs of cracking/flaking insulation then you can be pretty sure that the rest, especially under the spark plug covers will be shot to pieces, albeit that yours appears to have ben repaired. The problem is that there are likely to be other areas of the loom that are also flaking apart.

Take a razor blade and cut through the outer insulation on another part of the existing loom and assess the condition...if its a flaky mess, you're living on borrowed time

If you just ignore it, you risk the loom shorting out which can have the expensive knock on effect of blowing the coil packs and ECU etc etc.

I agree . Good place to start is at the maf plug. This is what mine looked like.

And just to put the willies completely in here's the ECU main plug...

There's no way of knowing till you cut the top off.



.

 

[jazzdude]

Ok I will have a look at the MAF sensor plug.

What is the current consensus regarding the best place to get a replacement loom?

I know there were deals in the past on here, but have there been many people who have successfully repaired their looms and avoided buying a new one?

Out here, W124's are still being used as taxis, and car electricians know them very well. A new loom out here though is over €1500 plus fitting, so you can see how keen I am to assess how bad my loom actually is.

 

[Williamwoo]

Ok I will have a look at the MAF sensor plug.

What is the current consensus regarding the best place to get a replacement loom?

I know there were deals in the past on here, but have there been many people who have successfully repaired their looms and avoided buying a new one?

Out here, W124's are still being used as taxis, and car electricians know them very well. A new loom out here though is over €1500 plus fitting, so you can see how keen I am to assess how bad my loom actually is.

Hi,

I would reiterate what the others have said. My maf connector was very similar to Druk's, and if you can see any cracking insulation anywhere on the loom, you should replace the whole thing I'm afraid.

I rebuilt mine. So long as you're reasonably competent with a soldering iron and that heat-shrink insulation stuff, it's not difficult but it is time consuming. The main problems are that you cannot buy all the various plugs and connectors separately so you have to reuse the existing ones. This means some rather fiddly soldering is required (patience is a virtue!). Also, there are many different colours of wire used in the loom and you will almost certainly have to improvise with new primary-coloured wires embellished with dabs of indelible ink to differentiate all the new sections of the loom.

Best tip? Take lots of photos and video before and during removal, and when rebuilding it, and document what colours you have replaced with what.

Good luck!

 

[jazzdude]

I will take my car to an auto electrician I know who used to work on mainly W124's and ask him. Hopefully it can be done without taking my car budget to new levels.

Don't get me wrong, I am now seeing where the magic is in these cars, especially my Cab, but even though it was given a thorough inspection when I bought it, I have spent a lot more in bringing it up to scratch than I initially budgeted for.

The words '20 year old' and 'sorted car' are further apart than I thought.

 

[Druk]

I made my own loom. Got a NOS 124 interior loom from ebay for £15 and canabalised that for colours and sleeving. A Dremel is your friend for getting into the sealed plugs. Here's the maf plug before and after. Re-sealed all using poly sealant.

Made my own coilpack loom from Maplin flexy cable and heatproof sheath.

.

 

[mejermy]

As williamwoo and druk, I remade my own, re-using the existing connectors. I wasn't happy with the fit and looks of the MAF when glued back together and obtained a MAF plug from a breaker for coppers and resoldered the new wire onto the very end of its wires. Should have done this with the original plug instead of cutting it open. I used Vehicle Wiring Products Ltd. Suppliers of auto electrical parts. to supply the wire and new ECU plug connectors. Their range of colours was sufficient to largely maintain the original codings. (No connection, just a customer).
Your car is going to be off the road for some days whoever does the rewire. I would urge you to consider doing this yourself. It a great way to familiarise yourself with the car, and the only efficient way to run these oldies is if you are handy at DIY. You also know what's done has been done correctly; so many garages seem not to have staff trained on older machines.

 

[jazzdude]

I took the car to a couple of auto electricians and they both said without a thought that they would not touch a rebuild on the loom.

Having said that they both didn't think a new loom was imminent. The fault does seem to be in the two wires that go to the temp switch but as the fault is intermittent, ie the fans didn't stay on today for example, that we should not even try to fix that part. This was because they thought that moving the loom around could damage it.

As the car seems to not display any other problems such as misfiring or other erratic behavior they both independently suggested that I leave it as it is for now but to plan to change the whole loom at some point in the next 18 months.

Would you agree?

 

[w124nut]

........Don't get me wrong, I am now seeing where the magic is in these cars, especially my Cab, but even though it was given a thorough inspection when I bought it, I have spent a lot more in bringing it up to scratch than I initially budgeted for.

The words '20 year old' and 'sorted car' are further apart than I thought.

Hi Jazzdude,

we are treading the same path regarding our cabriolets. Mine is also a 320 and bought her in January 2005

I bit the bullet and had my engine wiring harness renewed not because "things happened" but because the loom looked similar to those as shown above and I could not afford to do nothing and swallow the consequences.

I also had my car checked over before purchase from a reputable dealer (?) but since then have paid a small ransom in keeping her in tip top condition.

Whether you go down the road of DIY or a professional replacement of harness, IMHO, these cars are worth it.

 

[Vlad]

I took the car to a couple of auto electricians and they both said without a thought that they would not touch a rebuild on the loom.

Having said that they both didn't think a new loom was imminent. The fault does seem to be in the two wires that go to the temp switch but as the fault is intermittent, ie the fans didn't stay on today for example, that we should not even try to fix that part. This was because they thought that moving the loom around could damage it.

As the car seems to not display any other problems such as misfiring or other erratic behavior they both independently suggested that I leave it as it is for now but to plan to change the whole loom at some point in the next 18 months.

Would you agree?

Ultimately its your decision and I understand the cost implications, but if your loom has already needed repairs its likely the rest of the loom will be pretty much shot in other places.

You might get away with it for 18 months....or it could fail tomorrow and take the coil packs, ECU and the rest of the loom with it, which could end up costing you in excess of £2.5k+

I would suggest for piece of mind, that you get another part of the loom inspected and if its bad, bite the bullet and get the work done.

 

[jazzdude]

I asked the local dealer and with a discount the cheapest they can do it is €1150 (£960).

Are they cheaper there or does anybody know where a better deal can be found?

 

[trapperjohn]

That price is about right plus you get "at your door" (ish) back up.

 

[GP801]

That sounds pretty good. Our 280 was done by a main dealer in France when owned by the previous owner. Came to around !700 euros 4 years ago. Unfortunately it had already fried the ECU -£1400 + VAT for the part alone - so you could be getting a bargain.

 

[jazzdude]

That price was just for the loom, not including labour. Is it still good?