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Discussion Starter · #1 · (Edited)
Located this factory MB tow hitch setup at an auto recycler (junkyard). I didn't get to pull it, unfortunately, it was pulled for me. I am promised a refund if I need to return it due to being incomplete, etc.

But anyway...

Here's the hardware:



New bolts that I purchased from Bolt Depot:



Oris label on the receiver:



And here's a few shots of the wiring harness:







Now, what about these - are they factory/genuine Mercedes?





The connector for the trailer's plug, Pollack brand:





Pollak connector removed reveals this:




Here's what tells me this is a genuine MB hitch setup:
- The factory MB receiver was an Oris (in the USA anyway).
- The two big brackets shown are the correct MB brackets for reinforcing the bumper structure.
- The correct bolt guides are included.
- The wiring harness appears to be correct... however...

Here's what I'm not sure about:
- What's up with the transition from cloth to plastic wire wrapping? That doesn't seem normal MB behavior...?
- What's up with the Pollack trailer plug connector? Has this been added on after the fact?
- What is the big black box for? Has that been added on after the fact?
- Looks like it is currently set up for 7-pole trailer plugs. Is this standard from MB?

I've used the search function and read every thread I can find on "tow hitch", "hitch wiring", "towing" etc. I've saved lots of notes and lots of photos. I may have missed one or two good threads, but I believe I have located most of them.

Any pointers or info from those of you who are familiar with these hitches would be great!
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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It looks like it was set up for electric trailer brakes.
 

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That is a genuine MB OEM trailer hitch. Compare with this photo of a brand new kit.

Most internal harnesses are cloth-wrapped. The plastic tape is to help waterproof the harness after it exits the body.

Don't worry too much about the brands. Scores of companies make the parts that go into a Benz. Bosch make the ECUs, Hella make the headlights, and I guess Pollak make the trailer plug connectors. MB make the cars.
 

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1990 190E 2.6,.... 1998 ML320, 2005 ML500SE
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It's complete, including the electrical parts. Great find. Those parts are like gold.

1) Your missing the two screws that hold the Trailer Plug bracket to the bumper.
2) There are two bolts shown in the slots of the reinforcing brackets that I don't recognize and are not shown in the factory hitch parts diagram.
[EDIT] the two bolts are missing the guide bushings as shown on the other 2 bolts.
3) NOTE: Spacer Brackets only go in one way, see tab. Slight difference in angle of the tubes.
4) The shoulder on the new hitch bolts may be too long. Be careful to check clearance and use thread sealant.
5) The black box is the trailer light isolation module. It powers the trailer lights and isolates lights from the ML's wiring. (not electric brakes). Just plug in the wiring Plug shown (your pix 4 & 7) into the factory installed mating plug. See my post below. Truly Plug and Play.
6) When installing module you will see the oval rubber plug in the bottom of body where the module wiring goes out to the trailer wiring plug. Remove rubber plug feed wiring through from the inside to the outside and install the new oval rubber plug already on the wiring harness.
7) DON'T forget to install Fuse F18 (25A) in the engine compartment fuse box to power the module or else lights will not work.

Torque for hitch to bumper bolts, 118 ft/lb (160 Nm)
Torque for bumper reinforcing brackets, 36 ft/lb (49 Nm)

Mike
 

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PLEASE update your User CP to include at a minimum Model, Year and Location.

In your case it makes a difference in the location of the Isolation Module and the mating Factory installed Trailer Light Plug.
My 98ML is located behind a panel inside the rear cargo compartment behind the fuel filler door.
My 05ML is located behind outside left vent panel behind bumper cover just rear of left rear wheel.

Please forgive me it I have given you too much information.

Mike
 

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Discussion Starter · #6 ·
That is a genuine MB OEM trailer hitch. Compare with this photo of a brand new kit.

Most internal harnesses are cloth-wrapped. The plastic tape is to help waterproof the harness after it exits the body.

Don't worry too much about the brands. Scores of companies make the parts that go into a Benz. Bosch make the ECUs, Hella make the headlights, and I guess Pollak make the trailer plug connectors. MB make the cars.

Gotcha - that totally makes sense, the plastic tape is for protection of the portion of the harness that is exposed to the outside elements. Duh. Thanks.

I only mention the brands of the various parts because I'm trying to determine whether or not this is a complete and genuine MB setup, or if it is partially genuine but has been hacked into or modified. At this point, it seems to be genuine.


It's complete, including the electrical parts. Great find. Those parts are like gold.

1) Your missing the two screws that hold the Trailer Plug bracket to the bumper.
2) There are two bolts shown in the slots of the reinforcing brackets that I don't recognize and are not shown in the factory hitch parts diagram.
3) NOTE: Spacer Brackets only go in one way, see tab. Slight difference in angle of the tubes.
4) The shoulder on the new hitch bolts may be too long. Be careful to check clearance and use thread sealant.
5) The black box is the trailer light isolation module. It powers the trailer lights and isolates lights from the ML's wiring. (not electric brakes). Just plug in the wiring Plug shown (your pix 4 & 7) into the factory installed mating plug. See my post below. Truly Plug and Play.
6) When installing module you will see the oval rubber plug in the bottom of body where the module wiring goes out to the trailer wiring plug. Remove rubber plug feed wiring through from the inside to the outside and install the new oval rubber plug already on the wiring harness.
7) DON'T forget to install Fuse F18 (25A) in the engine compartment fuse box to power the module or else lights will not work.

Torque for hitch to bumper bolts, 118 ft/lb (160 Nm)
Torque for bumper reinforcing brackets, 36 ft/lb (49 Nm)

Mike
(1) Yep, noticed those screws are missing. I don't know what their specs are, so I will dig around in my spare screw jar and see if I can find something that works.
(2) Not sure what those are, either.
(3) Ok thanks.
(4) I actually ordered the same bolts that another member mentioned ordering for his own hitch, in another thread. I figured it was better to try them first, rather than re-use the one-time use factory bolts.
(5) Interesting. So currently there is no circuit for electric trailer brakes, correct?
(6) Thanks, think I saw that on a previous thread also.
(7) Gotcha.

Lots of good info, Mike, thank you. I'll never be unhappy with too much info :thumbsup:
 

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You are correct, I just glanced at the round connector and thought is was 7 pin.

Sorry for any confusion.
 

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You are correct, I just glanced at the round connector and thought is was 7 pin.

Sorry for any confusion.
No confusion. The connector is 7 pin, which is the convention for electric trailer brakes. But for trailer brakes one still has to connect one of those pins to a trailer brake controller.

Its far easier to make a 4 pin trailer connection starting with a 7 pin connector than the other way around. The picture of a new hitch kit shows a 7 to 4 adapter. Perhaps I should have looked in the trunk of my W164 before purchasing an adapter. :)
 

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Discussion Starter · #10 ·
You are correct, I just glanced at the round connector and thought is was 7 pin.

Sorry for any confusion.
Hmm. I see seven on the round Pollak connector. Six around the circumference, one in the center. What am I missing?
 

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Discussion Starter · #11 ·
No confusion. The connector is 7 pin, which is the convention for electric trailer brakes. But for trailer brakes one still has to connect one of those pins to a trailer brake controller.

Its far easier to make a 4 pin trailer connection starting with a 7 pin connector than the other way around. The picture of a new hitch kit shows a 7 to 4 adapter. Perhaps I should have looked in the trunk of my W164 before purchasing an adapter. :)

Ok. So the trailer brake controller will be an aftermarket item that I will have to get? Does it become part of the brake light circuit, or is it on a circuit of its own?
 

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Ok. So the trailer brake controller will be an aftermarket item that I will have to get? Does it become part of the brake light circuit, or is it on a circuit of its own?
I think you will find that a trailer with brakes has its own controller - you just plug it into the 7-pin connector and it will work. On the ML side, it's all wired up for trailer brake operation.
 

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Discussion Starter · #13 ·
I think you will find that a trailer with brakes has its own controller - you just plug it into the 7-pin connector and it will work. On the ML side, it's all wired up for trailer brake operation.
Ok gotcha. Have only ever towed an un-braked trailer or some with inertia brakes. Appreciate it!
 

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I think you will find that a trailer with brakes has its own controller - you just plug it into the 7-pin connector and it will work. On the ML side, it's all wired up for trailer brake operation.
Not in the USA. In Europe the law says the trailer must brake itself. In the USA we find it works better for trailer brakes to be controlled from the tow vehicle within reach of the driver who can tune the gain.
 

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Ok. So the trailer brake controller will be an aftermarket item that I will have to get? Does it become part of the brake light circuit, or is it on a circuit of its own?
In later models Mercedes-Benz ran a 4 wire pigtail from rear to under the dash near the driver's feet just like everyone else who is serious about building tow vehicles. Don't believe your W163 is prewired, it started sometime before 2009 W164.

To the 4 wire pigtail we connect something like a Tekonsha TBC which has an accelerometer inside and will proportionally brake the trailer based on how aggressive you are braking.

IMHO for a vehicle supposedly of Mercedes-Benz engineering reputation the TBC should be built-in and integrated with ABS, traction control, vehicle stability, and everything else. If integrated then it wouldn't need an accelerometer to know how hard you are braking. Hint: Ford, Chevrolet, and Dodge do exactly that.
 

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Discussion Starter · #17 ·
You got pretty lucky to get all this.

Agreed.

But, fortune also favors the well-prepared. I spent quite a bit of time chasing these parts - starting with doing a lot of research on this forum and elsewhere on the internet to get photos, part numbers, etc. Then, I was very expressive with more than a few junkyards, looking for and making sure I was getting the right stuff. And even after all that, I still came on here to make sure I got it right.

That being said, this forum is a great resource. Lots of great members that are knowledgeable and willing to share their expertise. Very cool :thumbsup:
 

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What is the max towing weight with-out having the reinforcing brackets? 3000 lbs or so?
 

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There is no rating for that. It is dangerous.

People have torn off bumpers with just a single snowmobile on a small trailer.
 

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Good source for trailer hitch

looking for a good quality, safe trailer hitch for my 2001 ML 320. Seen lots of different "designs" on different looking hitches. anybody got any suggestions for a good quality one that still available? i've heard you can't get the factory ones anymore for older ML 320's.

jay
 
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