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  #1  
Old 09-22-2003, 12:21 PM
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Question C280 Engine Wiring Harness Picture

Hi,

I'm pondering taking on the task of replacing the wiring harness in my C280 (it's visibly falling apart, not to mention the check engine light that just came on as expected).

I'm wondering if anyone has a picture of the harness (prior to installation) so I can get an idea of how many connectors and where they all fit in. I don't have the Mercedes shop manual to see it. I have wiring diagrams, but, I'm talking about finding an image of an actual harness that hasn't yet been installed.

I know that if I bought one, I'd have the answer to my question, but, I'm trying to decide if I should do it myself, or, take it in to the shop (UGH).

I'd sure appreciate someone's help.

Bill
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Old 09-22-2003, 01:27 PM
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I assume you're talking about a 104 motor / i.e. straight six. I don't have a picture but it's something most dealers would have in stock, since it's been such a problem. I put one in myself on a 3.2 104 motor and it's not that tough. It took about three hours but that was because I marked and numbered every connector and took my time. The truth is I overdid it - you don't really need to be so cautious. As I recall there's about 25 or so end points but there's so many unique connectors that you can't really go wrong. The wires are in maybe 4 or 5 different clusters and it's pretty obvious based on the length of the wires where they go. There probably only about 2 or 3 connectors/ wire lengths where you could possibly go wrong - so you mark those. The car started right up but later I noticed a lack of power, which was because the car had gone into the "limp home" mode as a result of the fault codes resulting from the wiring harness shorts. So I had to go to a shop and get all the fault codes erased, which was not big deal, and then the car ran fine.
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Old 09-22-2003, 01:54 PM
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C280 Wiring Harness

Yes, that's what I'm talking about, straight 6 (104 motor I believe).

So, this begs the next question...at least in your case, were the connectors reasonably accessbile.

I'm not too afraid of working under the hood (used to ALWAYS do my own work on my other cars, before the MB). The MB seems to have me a little more unnerved that I'd expect to be...know what I mean!? I don't want to hose it up and have to have it towed, but, the price I was quoted from the dealer seems to be FAR outweighing my fear of killing it myself by mistake..

Thanks for your replies (previous and future ones)!

Bill
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Last edited by bigpaws; 09-22-2003 at 02:42 PM.
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  #4  
Old 09-22-2003, 11:05 PM
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As posted earlier, replacement of the harness is a nice DIYed job for a weekend, where you are not pushed for time. The key is to lay out the new harness in roughly the same location as the old harness. Then you can slowly and methodically change out one connector at a time.

The dealer will charge you 5 to 7 shop hours to change out the harness; however, several posters on this board have described it as a 3 to 4 hour job.

In my case, I was able to get the dealer to change out my harness and we split the cost of the labor (done on the "good will" program). So, I ended up paying for about three hours of labor........which I felt was reasonable for the job. As it turned out, that was a wise decision on my part. Who would have thought that there would be a batch of new harnesses incorrectly marked! The dealer went through five harnesses which had the correct part number on them, but which were not for my engine! On the fifth try (he had a harness sent in from another parts depot), the part was the correct replacement harness.

Had I elected to save the money by doing it myself, I would still be out there trying to figure where I went wrong! And, my car would be out of commission.

The message here is to mark all the connections as you change them out, so that if you have to reverse your steps.........you can go back to the old configuration.
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Old 09-22-2003, 11:47 PM
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It seems like there was one connector under the intake manifold that was a little hard to get to, and of course you have to take the spark plug cover off to get to the coil packs, but other than that nothing too bad. I was quoted 3.5 hours by an independent shop, 6 hours by the dealer, and a friend said that he had witnessed it done in an hour and 15 minutes. This made me so curious I had to try it. If I had to do it again I think it would be under 2 hours. I suppose there's some risk of a tow job but you'd probably still be ahead.
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Old 09-23-2003, 12:00 AM
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just did it last week!

I happen to have just done the job last week on my 95 E320 (W124 with M104 engine). I ordered the part from Phil at the Parts Shop. According to the VIN I supplied him, I was supposed to have a certain part number on my harness. After I received it, I was about to put it in and had it all laid out along the old harness. Right off the bat I noticed one connector was different. As I went further down the harness, I saw some other discrepancies. After calling Phil and giving him the part number off my old harness, the replacement I had would not work. I sent back the old one and received the replacement which matched part numbers.

I just pretty much started at the large connector behind the battery and went one by one from there. It was actually pretty easy. Not wanting to be too hasty, I tried to make certain of the lengths of the wires, connector types, etc. before unplugging the old one. In my engine, there were 2-3 connectors that I had to do from underneath with my wife guiding my hand to the correct wire/connector but even those were not that bad. Overall, it took me about 3+ hours.

I happened to take a few pictures while I was doing it so I will try to post them here. (We'll have to see if I'm successful.) Here is a picture of the new harness. The large connector on the right is the one that plugs in behind the battery. The rubber-reinforced section plugs into the fuel injectors and plugs.
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C280 Engine Wiring Harness Picture-dsc01109.jpg  
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1995 E320 Wagon
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Old 09-23-2003, 12:03 AM
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Here is a picture of the air intake removed and the cover for the plugs removed.
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C280 Engine Wiring Harness Picture-dsc01110.jpg  
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Old 09-23-2003, 12:05 AM
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Finally a picture of the large connector removed and sitting on the battery tray (of course the battery was removed).
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C280 Engine Wiring Harness Picture-dsc01111.jpg  
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  #9  
Old 09-23-2003, 12:54 AM
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C280 Engine Wiring Harness Pictures

LuckyE320Wagon -

Thanks VERY much for your pics. Although my battery is in the trunk, I clearly get the idea from the pics you posted. I REALLY appreciate it.

I'm pretty sure I won't have the time this week to do it (work is killing me), but, in the next week or two (as long as it's still running, which at the moment, it still runs basically fine), I'll be doing it. I'll post with the results (or questions if they come up).


I do have a couple of questions left...

1. (I know, I'm full of questions...), would now be a good time to replace the plug wires, too, considering I'm going to have to mess with them anyway?

and

2. Can you buy precut plug wires that are the right length. I read that you have to buy a bunch of wire and cut it yourself and affix the ends (which I'm not confident about doing properly). I've never had to do that before.

oh...one more thing...

3. Should the coils be replaced, too while I'm at it, since, the car has 75k on it now, and they're original as far as I know.

Thanks MUCH!

Bill
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Old 09-23-2003, 08:44 AM
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My two cents in trying to answer your questions:

1. Should you replace the plug wires at the same time I replace the engine wiring harness? Absolutely. The plug wires see high voltage and are subject to heat and deterioration over their life. Be sure and also replace the plug connectors under the coils since they are usually the first part of the ignition wiring to malfunction (too much heat).

2. Should I cut wiring to fit, or can I buy the connectors with pre-cut wire? You can do it either way. Fully assembled wire sets can be purchased from Fastlane (about $100 +/-). Or you can purchase the resister boots and cut your own wires to length. Assembly is easy. You just cut the wire with a pair of diagonal cutters and "screw" the wire into the connectors which have a threaded post protruding from the connector. Use a little bit of silicone lubricant to wet the wire ends. This eases assembly and takes some of the twist strtess out of the wire as you screw it into the connector boots. Whatever method you choose.....be sure to replace both the wire and the connectors!

3. Should I replace the coils while I am at it? Not necessarily. Though the coils are subject to heat, they are a lot more stout then the wiring and connectors. They usually don't degrade in performance either since there are no wear and tear parts. They are also relatively expensive (about $300 for the set). They are also relatively easy to replace at any time, so you might want to save your money and not replace until they fail........which may be never!

Hope this helps.
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Old 09-23-2003, 09:25 AM
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My two cents in trying to answer your questions:

1. Should you replace the plug wires at the same time I replace the engine wiring harness? Absolutely. The plug wires see high voltage and are subject to heat and deterioration over their life. Be sure and also replace the plug connectors under the coils since they are usually the first part of the ignition wiring to malfunction (too much heat).

2. Should I cut wiring to fit, or can I buy the connectors with pre-cut wire? You can do it either way. Fully assembled wire sets can be purchased from Fastlane (about $100 +/-). Or you can purchase the resister boots and cut your own wires to length. Assembly is easy. You just cut the wire with a pair of diagonal cutters and "screw" the wire into the connectors which have a threaded post protruding from the connector. Use a little bit of silicone lubricant to wet the wire ends. This eases assembly and takes some of the twist strtess out of the wire as you screw it into the connector boots. Whatever method you choose.....be sure to replace both the wire and the connectors!

3. Should I replace the coils while I am at it? Not necessarily. Though the coils are subject to heat, they are a lot more stout then the wiring and connectors. They usually don't degrade in performance either since there are no wear and tear parts. They are also relatively expensive (about $300 for the set). They are also relatively easy to replace at any time, so you might want to save your money and not replace until they fail........which may be never!

Hope this helps.
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Old 09-23-2003, 09:35 AM
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earossi, Yes, that pretty much answers all my remaining questions. Thanks VERY VERY much!

I'm going to dive in as soon as I can, and see how it goes. I have more time than money, so, I guess, I'll just have to hold my breath and jump in. Sounds straightforward enough, although without the help of this forum, I'd have NEVER tried it on my own!

Thanks!

Bill
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Old 09-23-2003, 12:21 PM
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I agree on the coils - they don't seem to fail. I would say the spark plug wires are optional at 75k - they don't seem to fail much either and they are easy to get to if you leave for later. One thing to watch for is the allen bolts on the spark plug cover - they strip out very easily - I think just hand tighten - they don't need to be very tight.
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  #14  
Old 09-23-2003, 07:34 PM
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Ok, then...

Harness, wires and connectors, it is.
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