I've heard that the ML's are prewired for an electric brake controller, so I would not have to run any wires from the rear harness up to the front of the vehicle. Is there any truth to this?

I've looked uder the dash and behind the radio to see if there was any sort of wiring harness that could be used for this, but so far I have not been sucessful.

Does anyone know anything about this?

Ron, here's some info how to wire up a brake controller:

http://www.whnet.com/4x4/towing.html

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W163.154, M112.942, 722.662, ZF.970.402

Hi Wolfgang,

Is that your site? It's excellent. I've used it as a resource for years.

I know about that wiring diagram you referred me to as I had previously downloaded it. It led me to believe that I would have to run the wire to the front of the vehicle, but I seem to recall someone telling me the wire was already there. It seems not.

The section of the website that is entitled Shop Talk is extemely helpful to anyone with an ML.

Ron, glad you like the site. The ML is indeed prewired for a trailer, meaning one can plug the OEM MB trailer harness into the prewired connectors behind the left rear panels as described in this pdf:

http://www.whnet.com/4x4/pix/M-Class_OEM_Hitch2.pdf

However, this doesn't include the brake controller, which would need extra wiring.

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W163.154, M112.942, 722.662, ZF.970.402

I'm finally getting around to wiring my vehicle for the electric brake controller and I have a question.

The photo below shows the convertor box for the trailer hitch and the two plugs with several wires that go into it. Each plug has a orange wire which says on it "N28 #1660" which is what the instuctions to the link indicate is the wire to be cut and then go to the controller and back. The instructions say cut the wire after N28 but before the harness exits the vehicle thru the grommet.

So which orange wire do I cut? I think I cut the one with the green connector since it looks like it exits the vehicle thru the grommet, but I'm not certain. Can anyone confirm this

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Yeah, a little. The ML wiring is very cool in that on each wire (that I am aware of) there is printing on the wire which states where the wire "has been" and where it is going, and also (very cool) a circuit number which is also in the wiring diagram. HOW cool is THAT? So N28 is a component assignment that is used in the wiring diagrams, but I'm not sure what component that is, and on the wiring diagram, if you find the correct diagram for the system you're working on, you'd find this wire labelled #1660, takes away alot of guess work, but I don't know why you have wires at different connectors both labelled the same. Maybe if I had a diagram it'd make some sense. I'd look closer at these different orange wires and make sure you're not missing (not seeing) some of the lettering, you can report back on that. Does the instructions say what/where N28 is? If it that plug-in adapter you posted a picture of, you may just need to see which set of wires are leading outside the body to the trailer plug-in, that'd make the most sense. I thing there may be some wiring already going to the front dash area already.

Gilly

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Gilly,
That is very cool the wires having all those numbers on them. I’ve surely never worked on a car that has that much information on wires. I do have Aldata DIY and I printed the page that tells how to interpret all those numbers, letters and the like.

I double checked the numbers and letters on the orange wires, as you said, and they are as follows:
1-orange wire coming from the green connector in my photo is #1600 - -NG28- 6->X58-7
2-orange wire coming from the black connector in my photo is #1600- -NG28-2->52-B-6

Both of these connectors go into the black convertor box which is NG28. Since X58 is the 10 pole trailer socket and the orange wire coming from the green connector says it goes from NG28 to X58 that’s the one to cut. The other orange wire (the one going to the black connector) goes to X52 which is the 16 pole connector that the trailer light harness connects to.

Here is the link to the wiring diagram for the brake controller. I copied this link from Wolfgang’s post above, and it’s also on Aldata DIY. It’s http://www.whnet.com/4x4/pix/163_Brake_Controller_Wiring.pdf

Since the wiring diagram instructions say to run a wire to the front maybe the one up front by the dash will not work or doesn’t exist. It just seems odd the instructions do not say to tap in the orange wire in the dash. I will say that there is an orange wire going from NG28 to X52 and it must go somewhere but then even if it did connect to the brake controller it would still need to get back somehow to complete the circuit from the controller.

The other photo shows a connector with three wires, but I can not get to it enough to read any coded information on it and I don’t think it has to do with the trailer wire but who knows.

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On the 3 wire connector you posted a picture of, you could always cut the nylon wire tie and unwrap some of the cloth wrapping and there should be info on those wires as well to help determine what those wires are for.
I am in agreement with your observations. On the ML's where we had someone wanting to install trailer brakes, we never actually had to do the installation on that part, it was always being done elsewhere, but we had provided things like a copy of the wiring schematic after we did the basic hitch installation, so I can't be sure about what I am saying about the wires possibly being pre-installed.
Gilly

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I figured out what the connector with the three wires going to it in my last photo is for.

See the drawing of the connector below. It's for that external rear wheel and tire carrier available in Canada and Europe.

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I just finished installing the brake controller on my '98 ML. I made an error in splicing into the brake wire and just wanted to post clarification for the next person.
Reach into the wiring compartment at the back of the truck and find the point where the trailer wire harness enters the vehicle. Slide your hand up the harness until you reach a hard rectangular unit covered in a black plastic sheath. That sheath covers a small circuit board. Remove the black cover, I used a small pair of scissors. Find the orange wire that leaves the circuit board and then exits out to the trailer plug. Cut that orange wire. The end of wire the leaves the circuit board is the brake signal to the brake controller. The other end of the cut wire is where you tie in the brake controller output. I found it easier to push the wire harness and circuit board out the bottom of the truck, make the splice from underneath, wrap the circuit board in electrical tape, and then push back into the truck.

I skipped the entire MB wiring harness purchase and installation and had my hitch guy just install the controller, seven-way Bargman plug and run the wires accordingly as needed. The harness and associated parts from MB were priced to so high it was not worth the time, money and effort. To date no issues with the install.

-Kevin

My trailer connector wiring hitch wiring is set-up correctly and works properly for non LED lights on both the tow vehicle and the caravan.

I have installed LED brake/tail & indicator lights on the caravan.

These work properly when energised but at the same time they all continue to flash on & off non stop all of the time.

The rear of the van lights up like a Christmas tree.

I have fitted an electrical wiring harness into the circuit with four load resistors to "fool" the "smarts" in the car into thinking the LED's require a higher load.

The four resistors are wired into the Brake, Tail light and each indicator circuit.

The flashing light problem still persists.

The colour code for the electric wires are: Earth - white, Brake - red, Left indicator - yellow, Right indicator - green, Tail light - brown, Trailer brakes - blue.

I note that there is a Black wire designated for reversing lights. This is not connected as it is not needed but there is a small current output from the car.

Question (sorry it took so long to get here) - if I connected another load resistor to the Black wire, would it fool the car computer into thinking there is a power demand on this circuit and stop the flashing light problem?

I understand that incompatibility with LED lights is a common problem particularly with European cars.

Thank you, all replies will be appreciated.

Peter.