R-class hitch install with Factory wiring harness - Page 3 - Mercedes-Benz Forum
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post #21 of 112 (permalink) Old 05-06-2012, 03:36 AM
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Radodrill thank you for the help!

OK
The harness is part number A164 440 15 39
SAM part number is A 164 900 54 01

I have attached images and the plug at the end of the harness will not fit the SAM.

The other wires Red 12v+, Brown ground, green 2 wire plug for electronic brake is clear to me but the mystery here is why the SAM plug is wrong.

I looked at the end of the SAM plug on the harness and only 6 of the 14 pin holes has wires to them.

Not that it matters at this point but I have no relay schematic so it is unclear where U and K positions are.

I swapped the old SAM back and the power seats work again. I am not sure why the new SAM made them stop working. Does it need programming maybe?
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post #22 of 112 (permalink) Old 05-06-2012, 04:09 AM Thread Starter
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Quote:
Originally Posted by Mellow52 View Post
I have attached images and the plug at the end of the harness will not fit the SAM.
Hmm then MB must have changed the plug for the trailer wiring harness and the ML part number I listed appears to be for the older one. The other possibility is that the wiring harness was the non-US part (rear SAM and harness are different for the US variant); although the codes indicated that it was for the US model.

I just re-checked the Mercedes EPC (Electronic Parts Catalog) and it looks like part A 164 440 64 34 (what I had quoted for the GL class) is also used on the ML class with the correct rear SAM I had listed.

And when a new rear SAM is installed, it will have to be programmed to ensure that all the connected devices are working correctly; so apparently your power seats are in fact driven by the rear SAM.
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post #23 of 112 (permalink) Old 05-06-2012, 04:30 AM
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Well this is a mystery. The manufacturing date on the harness is 1/24/2012. If the plug on the harness changed then it is safe to assume the SAM had to change as well in the ML otherwise where would you plug it in?

Do you suggest I should try the GL cable? I am not sure if it would be possible to find the 'old style' ML cable if there is such a thing.

My fear is that the GL cable arrives and also has the wrong connector. I know most dealers will not accept back any electronic parts so I will test my MB dealer on Monday with fingers crossed.

Any hints for the location of U and K relays? My manual or the little booklet in the spare tire makes no mention of these potions. I also looked on the fuse/relay housing/block and there is no U or K markings.
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post #24 of 112 (permalink) Old 05-06-2012, 04:48 AM Thread Starter
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The manufacture date of the harness does not translate to the production time of the actual vehicle as the harness is still made as a replacement part.

That GL harness should be the correct part but unfortunately I have not been able to find a picture of it to be 100% certain.

The pamphlet in the tool kit only lists the fuse positions; but there are markings beside each of the relay sockets. The 2 relays are on the end opposite the +12V post. I'll try to see if I can find a diagram that has the relay positions marked as well.
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post #25 of 112 (permalink) Old 05-06-2012, 05:02 AM
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OK I will try the GL cable and take the SAM with to make sure it 'marries'. I will let you know the result.

So what is your driving style towing with your R-class? It has no Low range selector so I am curious what the best practices are to be as gentle as possible on the transmission.

Again, your time and help with this is very much appreciated.
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post #26 of 112 (permalink) Old 05-06-2012, 05:32 AM Thread Starter
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To be honest, we got the hitch more for accessories (bike racks, cargo carriers, etc), but also to have the ability to tow as we will occasionally need to tow in the future.

That said, the most important thing for towing with the R-class is to be mindful of the fact that the (aftermarket) receiver is low compared to most SUVs so you should be careful when going over bumps and at the bottoms of hills; this is more an issue with hitch accessories than with a trailer as you'll want the ball mount in the rise orientation.

Other than that, you'll want to make use of the shift range restrictions (paddles on the back of the steering wheel) to keep the engine within it's power band and not allow it to go into overdrive; i.e. don't let it shift to a gear that would allow the engine to drop below ~2500 RPM, particularly when climbing hills. This is also very useful going down hills as the engine will act as a brake thus not putting as much stress on the breaks. The reason for this is that at low RPMs the engine doesn't have nearly as much power and the load of the trailer weight would add significantly more stress to the engine than when operating within the power band. Without a trailer (or heavy load in the trunk) it's ok for the car to go into overdrive as this translates to better fuel economy.

Another point to be aware of is that for the 2009 R-class Mercedes put in a larger intercooler (primarily as a precautionary measure) since that was the year they started offering the tow package as a factory option. As such, be sure to keep an eye on the oil temp to be sure that it doesn't overheat; although this shouldn't be an issue unless you're towing a fully loaded trailer through the desert.

Last edited by radodrill; 05-06-2012 at 05:44 AM.
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post #27 of 112 (permalink) Old 05-06-2012, 09:44 AM
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Radodrill thanks for the tips. I just completed the hitch install and it went with out a hitch with a good set of tools everything goes smooth.

Now just to get that pesky wire harness to work and install the electric brake unit.

The pop up camper I will be towing weighs about 2600lbs so not that much heavy pulling. I will be sure to keep an eye on the oil temp.
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post #28 of 112 (permalink) Old 05-06-2012, 10:13 AM Thread Starter
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The installation of the receiver is pretty easy; it's just an issue with the wiring, particularly having to hassle with dealers who don't know squat.

And the R should pull that 2600 lb trailer no sweat.


Side note: I just wanted to edit the first post to state that the part number I had listed for the ML harness won't work, but the forums won't let me guess I'm going to have to find a mod to PM.
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post #29 of 112 (permalink) Old 05-06-2012, 01:46 PM Thread Starter
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found a diagram of the rear fuse box
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post #30 of 112 (permalink) Old 05-06-2012, 06:02 PM
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Quote:
Originally Posted by radodrill View Post
found a diagram of the rear fuse box
Fantastic! Thank you for the relay diagram. I spent days looking for it and even my MB dealer could not tell me the positions, what a surprise.

Radodrill on our first night of camping with the pop up camper I will have a cold one on you.

I will report back with pictures about the harness as soon as it arrives. My MB dealer normally takes 2 days to get the stuff I need.
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