R-class hitch install with Factory wiring harness - Page 2 - Mercedes-Benz Forum
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post #11 of 112 (permalink) Old 03-08-2012, 01:11 PM
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Vehicle: 2008 R320 CDI, 2006 smart fortwo cabrio, 1983 240D, 1982 300SD, 1980 300SD, 1978 280SE EURO
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Wow, very well researched and congrats on bypassing your dumb dumb dealer! So what can those of use with the older 08's do (my vin is 64XXX), I have bought the modulite unit but waiting for warm weather to install, again I hate the idea of crude installs with parts that might last 5 years...can I install the updated sam or it will not communicate with the older cars?
I use my hitch almost every trip for a cargo tray, but will need it to tow utility trailers this summer for sure and they have led lights all around.
Greg
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post #12 of 112 (permalink) Old 03-08-2012, 03:35 PM Thread Starter
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Originally Posted by houseofdiesel View Post
Wow, very well researched and congrats on bypassing your dumb dumb dealer! So what can those of use with the older 08's do (my vin is 64XXX), I have bought the modulite unit but waiting for warm weather to install, again I hate the idea of crude installs with parts that might last 5 years...can I install the updated sam or it will not communicate with the older cars?
I use my hitch almost every trip for a cargo tray, but will need it to tow utility trailers this summer for sure and they have led lights all around.
Greg
I am not certain, but I'm guessing that the R-class with VINs prior to A068595 simply cannot accommodate the OEM Receiver, while the wiring is probably the same.

Take a look at your fuse table (located in the tool kit in the spare tire well); if this clearly states location 70 is for trailer or hitching mechanism, then the updated rear SAM and wiring harness should work.



For LED trailer lights, you'll probably need a bulb-out bypass cable or wire up your own. All the cable/adapter does is connects 100 Ohm 2W resistors across the left stop/tail, right stop/tail, and marker light outputs (i.e. in parallel with the bulbs) so that the car recognizes the presence of the trailer as the LED lights don't draw enough current for the car to detect them.
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post #13 of 112 (permalink) Old 04-10-2012, 04:35 PM
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Thank you for the excellent post on the factory wiring harness. I have a 2007 r320 cdi. Today I installed it without any problems. I ordered the parts from Getmercedesparts.com and they came to about $150 including shipping. I did not need to upgrade the rear SAM. I enabled the trailer function in STAR and enabled the trailer sensing on the gateway. The only thing I could not enable was the LED trailer light feature on the SAM screen. My SAM hardware was dated from 2005 and the software 2006. It works perfectly.
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post #14 of 112 (permalink) Old 04-10-2012, 04:52 PM
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Originally Posted by radodrill View Post
The Hidden Hitch receiver was ~$200, wiring harness was ~$70+tax, plug was ~$40+tax, and the rear SAM was ~$400 ($600 incl tax and installation), and the relays were ~$27 and ~$32; so about $1000 total.

I installed the receiver and wiring harness myself, but had to have a dealer install the rear SAM as that also had to be programmed.

I don't have any pictures of the install process, but I can take a few of the underside and electrical connections.
radodrill.

My 08 built in Dec. 07 so I do not need the new rear Sam ($600).
So if I install the hitch without reprogram by the dealer, it will cost me around $400. Is this correct?

2008 R350 4 Matic w/P1 package/7 seater/Ipod/Front heated seats/ Retrofitted OEM GPS Navigation / 10.2" LCD Overhead Mobile Video system w/ 30 Sega Games, Wireless HeadPhone, hard wired to OEM HK sound system, B/U Camera integrated W/ 6 Disc DVD Changer , hard wired Passort Escort X8500, Mtec HID, 17 SMD LEDs city lights.

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post #15 of 112 (permalink) Old 04-10-2012, 05:42 PM Thread Starter
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radodrill.

My 08 built in Dec. 07 so I do not need the new rear Sam ($600).
So if I install the hitch without reprogram by the dealer, it will cost me around $400. Is this correct?
No matter what, the central gateway and rear SAM will have to be programmed to recognize the trailer wiring. I do not have access to a Star Diagnostic System, so I had to rely on the dealer to program and the local dealer claimed the the SAM that came with the vehicle would not accept the programming for a hitch so it was replaced; though based on some comments here, apparently some of the pre-09 R-class do have a hitch-compatible rear SAM.

Provided your rear SAM is trailer compatible, you'd only need the mechanical hitch, wiring harness, relays, bumper plug, and possibly a mounting bracket for the plug socket. These items together will cost around $400
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post #16 of 112 (permalink) Old 04-13-2012, 05:32 PM
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Originally Posted by baliunas View Post
Thank you for the excellent post on the factory wiring harness. I have a 2007 r320 cdi. Today I installed it without any problems. I ordered the parts from Getmercedesparts.com and they came to about $150 including shipping. I did not need to upgrade the rear SAM. I enabled the trailer function in STAR and enabled the trailer sensing on the gateway. The only thing I could not enable was the LED trailer light feature on the SAM screen. My SAM hardware was dated from 2005 and the software 2006. It works perfectly.
Which hitch did you install?
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post #17 of 112 (permalink) Old 04-14-2012, 04:59 PM
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Car came with a hitch installed already. I think the prior owner used it as a bike rack.
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post #18 of 112 (permalink) Old 04-15-2012, 08:03 AM
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Originally Posted by baliunas View Post
Car came with a hitch installed already. I think the prior owner used it as a bike rack.
Do you know what brand it is, or could you post a pic or two?
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post #19 of 112 (permalink) Old 05-05-2012, 06:10 PM
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I have a R350 (2007) and a pop up camper that has electric brakes.

I upgraded the SAM ($418) and got the ML-class A 164 440 15 39 harness. I installed the SAM but are not sure where to plug the harness into?

The ML-class A 164 440 15 39 harness has the following wires.

1) White 14 pin (some empty pins) plug - thought this had to go to the SAM but there is no spot for it.

2) Green 2 pin plug

3) Brown wire (ground ?)

4) Red wire that ends in a 20amp fuse holder with fuse (+ ?)

I have the Prodigy P2 electronic brake controller.

I also made the mistake to not disconnect the battery when I swapped out the SAM and now the power seats do not work. I will have to check it out in he morning.

What a nightmare.

Any help would be appreciated.
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post #20 of 112 (permalink) Old 05-05-2012, 10:13 PM Thread Starter
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Originally Posted by Mellow52 View Post
I have a R350 (2007) and a pop up camper that has electric brakes.

I upgraded the SAM ($418) and got the ML-class A 164 440 15 39 harness. I installed the SAM but are not sure where to plug the harness into?

The ML-class A 164 440 15 39 harness has the following wires.

1) White 14 pin (some empty pins) plug - thought this had to go to the SAM but there is no spot for it.

2) Green 2 pin plug

3) Brown wire (ground ?)

4) Red wire that ends in a 20amp fuse holder with fuse (+ ?)

I have the Prodigy P2 electronic brake controller.

I also made the mistake to not disconnect the battery when I swapped out the SAM and now the power seats do not work. I will have to check it out in he morning.

What a nightmare.

Any help would be appreciated.
First off, what is the part number of the upgraded rear SAM? We had part A 164 900 54 01 installed (used on the R, ML, and GL class) and it does indeed have the connector for the hitch wiring.

The harness has a multi-pin connector with 4-6 wires going to it that connects to the rear SAM, which is hidden behind some trim on the right side of the spare tire well. If you pull out the spare then remove the plastic liner on the right, it'll be located right underneath the trunk floor. I found a picture of the rear SAM online and highlighted the plug for the trailer harness (see attachment).

The orange (maybe sort of brown) wire with the round crimp terminal at the end is indeed the ground. If you remove the access panel on the right of the trunk (right behind the tail lamps) there is a screw with a nut on it for the grounds (should already have a few ground wires attached to it).

The red wire with the brown 20A fuse fuse holder is the +12V to the bumper plug (battery power). This should be connected to position 70 of the rear fuse box (in the spare tire well) and, as I stated in the first post, will only receive power if the relays are installed in positions U and K.

The remaining connector on the harness goes to the brake controller. As you say this is only a 2-pin connector, one wire is obviously the brake signal from the rear SAM and the other is the powered signal to the bumper plug. You'll need to connect these along with a +12V and Gnd to your brake controller. I'd probably route a length of 16-4 wire from the rear to the driver foot well so that you can have the brake controller accessible while driving.
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