SL600 wiring harness repair (cracking insulation) - Mercedes-Benz Forum
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post #1 of 254 (permalink) Old 04-13-2010, 07:46 AM Thread Starter
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SL600 wiring harness repair (cracking insulation)

Since I have been repairing the cable harnesses in the 129 and tend to write the same information over and over again I thought it was time to do this one and for all. Since I am not a native English speaker you have to bare with me.

My knowledge only stretches as far as SL600 and -93/94 since I have owned a -93 and currently owns a -94.

What it is al about is that the insulation on the wires crack and crumble in certain harnesses in the engine compartment. Reasons for this is discussed in many places and I am not going to dig any further into it, the problem is there, MB f****d up, fix it.

My research shows so far there are 4 different harnesses that have this problem and I will address them one at a time.

When I found the problem I checked some prices at MB and I would guess in Sweden the price for them all would be close to $8000 (estimate) just in parts, labor not included.

I bought my wires at Elfa, but can be bought anywhere, just choose a wire that can stand high temperatures and chemicals. I also used a lot of heat shrinking tube with heat glue on the inside which makes it waterproof, some cable ties and everything you need to do proper soldering.

Strongly recommend having a digital camera to document it all, insulation crumbles and is really difficult to see what the colors on them were. Pictures helped me many times. Marking the wires is not a bad idea.

And last but not least, patience as an angel and a few really nice beers does not hurt, as usual best beer is Czech, but also an Irish Guinness or a Belgian Gulden Draak will do. German beer only got me in a bad mood as I was emptying supply of swearwords over Germans who could not have chosen good wires to start with.


As I said, I will address each harness in a new post and try to explain my conclusions, feel free to correct me. There are probably several ways of doing it, this is my way.
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post #2 of 254 (permalink) Old 04-13-2010, 08:08 AM Thread Starter
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We begin with the largest of the sinners, called Enginge Harness. This runs from the computer box at the far back of the engine compartment on the passenger side on top of the engine to the front of the engine. Remember, this is for V12.
This is the easiest one to inspect, just remove the cover on top of the engine, 4 Allen bolts (size 4 I believe). Under the cover you will se the wires, if you see cracks, well congratulations, you got your spare time laid out for you for about a week. If not, bend and abuse the wires to see if the crack. If not, you are lucky. I would say that if it has not been replaced, there will be cracks.

This harness can be completely removed from the car by loosening all the connectors to the injectors, 12 of them, and also a few connectors in front of the engine. The harness runs through the wall in te rear of the compartment, the top of the wall needs to be taken out, 2 screws ad then runs to a 40-pin (about) connector next to the computer box.

Looks like this when out of the car:


It is possible to take the 40-pin connector apart, even if it was not meant to be taken apart again. All pins are crimped on the wires, I soldered new wires on all the pins, took all of the old wires out and put the new ones in. All of the parts has part no, should be possible to get new ones at MB, but that would probably be more expensive then buying a new harness.

The larger connectors in front of the enginge need to be cut open, I used a Dremel tool, soldered the new wires in place and then glued the connectors with epoxy. I checked the price for one of the connectors at MB, about $150.

In short, replace all the wires pin to pin with new wires.

Result:


I have rebuilt one of theese in my -93, I have also seen the problem in another -93, my -94 already had the harness replaced to a brand new one.
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post #3 of 254 (permalink) Old 04-13-2010, 02:55 PM
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Fascinating write up - hope I never need to use it though!

Thanks
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post #4 of 254 (permalink) Old 04-14-2010, 04:24 AM Thread Starter
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Well, next one in this tragedy...

ETA=Electronic Throttle Actuator

V12 has 2 of theese, one for every intake/cylinder row, as far as I know the others have 1. The one on the drivers side acts as a "master" controlled with the throttle wire and then signal transferred to the passenger side (slave). So, more cables and crap on the drivers side then the passengers side one.

The passenger side is quite easily inspected on SL600 and if this one is bad, the other one is too. Remove LMM/MAF and for makin it easier aslo the air filter box (not needed, but easier). Remove the large rubber bend and then the ETA is fastened with 4 Allen bolts, nuber 5 I think. Also a few rubber hoses, there is a gasket between the ETA and the intake, might brake if not careful, but costs about $3 at MB.

Follow the harness from the ETA to the connector under a cover and remove the ETA from the car. First it should be cleaned with some kind of solvent/alcohol, should be nice and shiny on the inside.

There are 2 covers, one on each side, you only need to open the one with the harness, 5-6 torx screws, there is a gasket here aswell, don't know if you can buy this one, be careful not to break.

Under the cover you can see how bad it looks, probably like this:


As you can see in the background there are thinner pastelcolored wires, theese are for "internals" of the ETA and seem to be of better quality. Compressed air will clean out all the cracked insulation.

Try to identify all the wires, the have a letter printed on the circuitboard and the pins in the connector are numbered.

Be careful to identify theese two, this is the mains for the ETA-engine and it has a + and - lead, NOT MARKED, and I believe that you don't want the engine to be running the wrong direction:


The connector needs to be cut open, the first one i did with a knife and a small hammer, cut a lot, tap the knife with a hammer. This will cost you a lot of cuts on your hands aswell as twice the amount of beer and swearwords. The later ones I cut open with a Dremel.:


You only need to cut through the outer cover and then pry it open with a screwdriver. Identify wires as you touch them they will crumble:


Where the cable enters the housing is a little bit tricky, it is glued to the cable, in worst case, cut the wires and drill them out of the sealing rubber ring. New wires is starting to come in place, I didn't care much to follow the old color of the wiring, made a new diagram wich says what old color is the same as the new color:


New wires for the connector:


Heatglue from a gluegun works perfectly, justbuy glue that can take a little bit higher temperatures because of the engine heat.
Why heatglue? I wanted to try theese out before sealing them of for all future and heatglue is easily removed and seals properly. Besides, the connector is in a socket and cannot go anywhere, so for theese heatglue is perfect, if epoxyglued it will be tough to take apart again:


Just put it back in the car and get going with the drivers side, in principal the same thing, just a few more wires and also the throttle wire with control arm. The arm is easily pried out of its "ball", it is spring loaded so no worries. A little bit trickier but in general same procedure.
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post #5 of 254 (permalink) Old 04-15-2010, 05:57 AM
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As GUSMB says, using a Dremel tool with a thin, abrasive disc to open the connectors is the best method. I did this for my MAF connectors, and it worked great.
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post #6 of 254 (permalink) Old 04-19-2010, 06:18 AM Thread Starter
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Since I had a few questions I will try to answer them here for everyone to see:

What gauge wires?
There are at least 3 different gauge of wires, since we use metric system in Sweden and since I do not remember what I used, I am not going to write any numbers, just measure them or bring a piece with you to the shop and the will set you up with the correct ones. I bought thicker ones by accident, doesn't really matter, but is more difficult to work with. As long as you do not go for thinner ones.

Colors of wires?
There are about 35 wires with different colors in the main harness on otp of the engine, I could not find matching ones for all of them, I tried to match as many as I could. I made my own schematic (Excel-sheet), containing old color = new colour basically.

What do I need?
Good sheating for the wires, I bought some that resisted chemicals and was suitable in a high temperature environment. They are black, weaved and silicone coated. But anything that will withstand the environment should do. You pretty much have to figure out lengths and diameter of theese and you will need quite a few different ones.

Wires, any wire with correct gauge or thicker that can withstand temperatures and chemicals will probably do.

Heat shrinking tube, I use the one with heatglue on the inside, makes joints waterproof and also strengthen joints, you will need MANY different measurements.

Glue, I prefer heatglue (easily removed) and epoxy (makes it completely waterproof), just remember to read up on epoxy and wear gloves.

Tools, you need a few basic tools, not going into this, but a Dremel with a cutting disk is really handy when it comes to open up connectors.

Soldering, well, everything you need to solder, remember to use flux on everything, if you want to do it properly wipe off the flux afterwards with alcohol.

Zip ties, many wires are held in place by zip ties, good to get a set with many different ones.

Band-Aids is good to have and as mentioned above, plenty of beer and patience...
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post #7 of 254 (permalink) Old 04-19-2010, 07:10 PM
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Thanks for more details. I am going to be tackling this harness immediately. I do have a questions about access to the connector that connects back at the alluminum box on the passengers side. How do I pull the connector through?
Do I need to remove the fan box etc or do I pull the wires through the other way? If I need to remove the box with the blower what is the correct procedure to remove this? Also, I have decided to go with GLX (higher temperatrure and chemical resistant wire. I will buy as many different colors of this wire and then match up as best as I can using a excel spreadsheet key as you suggest.

Thanks,
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post #8 of 254 (permalink) Old 04-19-2010, 11:44 PM Thread Starter
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Quote:
Originally Posted by scasey View Post
Thanks for more details. I am going to be tackling this harness immediately. I do have a questions about access to the connector that connects back at the alluminum box on the passengers side. How do I pull the connector through?
Do I need to remove the fan box etc or do I pull the wires through the other way? If I need to remove the box with the blower what is the correct procedure to remove this? Also, I have decided to go with GLX (higher temperatrure and chemical resistant wire. I will buy as many different colors of this wire and then match up as best as I can using a excel spreadsheet key as you suggest.

Thanks,
The connector is located on the right side of the computer box, the wiring runs in front of the airbox in a small gap to the metal plate, here you can see where the harness goes through the "wall":


It is not essential to remove the airbox, but will make things easier, you have to remove the cover for the airbox though. The "metal plate wall" kan be separated, one screw on each side holds it in place. Then you don't have to pull anything through , just lift it out.

If you can get different colors for them all, great, I just didn't have time to look into it anymore, I even think a few of them have the same color, but I marked them out clearly.
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post #9 of 254 (permalink) Old 04-20-2010, 07:53 AM Thread Starter
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And the show goes on....

LMM/MAF wiring harness, this can be the most difficult one. Depends on how bad it is and how much work you want to put into it.

In SL600 there are 2 LMM, the wiring to these tend to be in the same shape, or worse then the others.
To inspect these you need to cut the sheathing open close to the connector to see the wires. But if the others are cracked, these will probably be as well.
The worst part is that these cannot be unplugged from the car, they start inside the computer box and go to the LMM without any connectors.

When inspected and cracks confirmed, cut the harness wherever suits you, doesn't really matter as the easiest way is to make a new one long enough so you cut it to be the correct length afterwards. In the picture you can see that the wires aren't that pretty, extremely difficult to see colors of the wires. I manage to do my own schematic if needed:

Remove seal and locking ring:


Open up the connector in whatever way you feel like, I use a Dremel:


Tidy the connector up and solder new wires in place:


Protective sheathing and heat shrink tube on EVERYTHING:


Sea the connector with glue, heat glue doesn't work that well for these, but easily removed and replaced by epoxy later on for me:


Heat shrink tube with thick walls and heat glue on the inside makes it waterproof:


The finished result, we will get to the length of the harness later on:


In my -93 I noticed that the driver’s side was not cracked, so I just put new sheathing on. Passenger side was a catastrophe, redid it as above and traced the wire towards the computer box until I found a place where the wires were all good and no cracks in sight. I spliced and staggered the joints in place:

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post #10 of 254 (permalink) Old 04-20-2010, 07:53 AM Thread Starter
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Above is the easy way to go, works just fine, if you can find somewhere the wires are all good, go for this. BUT, there are no guarantees that the rest of the wire will crack as well. On the -94 the other hand it was way worse, first of all both sides where horribly cracked. When trying to find a good place to splice into the harness I ended up right back at the computer box.
This is not a problem on the passengers, not much needs to be removed, on the drivers on the other hand, a lot has to be removed. In short all this crap:


The harness runs in front of the fan:


Remove lid from computer box:



Gut it, remove everything:


Loosen all the sockets and remove the aluminum frame:


By now you should have noticed that the wires run through the walls of the box with a lot of other wires. I found it to be too much work if not impossible to run them the same way as before, so I decided to drill new holes.

Rubber seal for harness entering the computer box, find correct wires underneath the sockets, cut them pretty close to the actual pin, but save a short piece of wire to solder to. Do not forget shrink tube:


Kinda messy, but works well:


Company is always nice:


Then all you have to do is get everything back in the car and do a test run, or inspect next harness and continue with the repairs.
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