UberFusion

I want to put a trailer hitch on my wife's 2012 ML350 Bluetec. I think I have the hitch all figured out (Curt # 13117) but now I'm trying to figure out the wiring...

Having done this approach previously with other vehicles , my plan is to buy the Curt wiring module (eg #56195) and splice into the vehicle wiring near the actual stop, left/right turn signal and tail light bulbs.

Since this module also has a wire that goes to the battery + terminal, the trailer lights will draw power directly from the battery and therefore won't affect the current draw for the ML350 bulbs (and consequently impact any possible sensing the ML350 may or may not be doing).

Does anyone have any experience / suggestions on this wiring approach...?

Haven't dug into the actual rear light wiring yet but I assume it shouldn't be too hard to access the bulbs and wires...?

Many thanks and regards, Glen

stas2007

I am actually looking into the same set up and am planning to install it in a few weeks.(still cold here in Boston)
My plan is to use Curt 13117 as well and use modulite 119192 for lights.
Modulate 119192 has the following specs, which seem to match what I need:

• The unit is rated for up to 4.2 amps for Turns/Stops circuits and 16 amps for the Taillight circuit
• Universal ModuLite designed to be used on most vehicles plus the hard to wire vehicles
• Draws power directly from the vehicle battery and uses less than 5mA of the vehicle circuit for sensing to turn the trailer functions on and off
• Will work with either LED/Incandescent bulbs (vehicle & trailer)
• Has integrated re-settable Short Circuit and Overload protection, to safeguard itself and the tow vehicle from shorts and installation wiring mishaps
• Designed not to send feedback thru the vehicle circuits
• The trailer brakes will override the hazard lamps when the brake is activated
• Advanced circuitry works in all standard applications as well as vehicles with ST and STT pulse width modulation (PWM) systems
• Interprets/decodes multiplex signal inputs (i.e. Audi, BMW, Mercedes and VW)
• Will not work with vehicles with low-side switch
• Can be used on a 2 wire or 3 wire system
• All solid-state components in potted encapsulation

I am not a pro when it comes to Hitch installs, but considering ML has LED taillights modulite 119192 seems like a good match.
Check out this thread, in the middle of the page there is some reference installing a hitch on 2012 ML:
http://www.benzworld.org/forums/w164...h-install.html

UberFusion

Appreciate the reply Stas2007.

Since I'm in Toronto I couldn't agree more about the weather - I'm sure it will be at least several more weeks before I'm brave enough to get started.

Looks like you and I are on the same track. I'll look more into the modulite 119192.

If you go to (I think that's where I saw it) the Curt web site and search on 2012 ML350... there is some installation directions on the hitch, and they look quite straight forward...

I need to look more into the 350's rear lighting since I've seen some references to PCM (Pulse Code Modulation) being used in the lighting circuitry, but I'm not sure how... Being an electrical engineer I would presume for some kind of brightness control, but in any case the adapter module (curt or modulite ??) should be able to handle this (ie. essentially filter it out and still be able to 'trigger/drive' the turning on of the trailer lights.

Would like to stay in touch with you over the next month and compare notes on ideas, progress, issues, solutions - you name it !! LOL

Cheers, Glen

UberFusion

OK - making good progress.

I ordered and rec'd last week the CURT 13177 hitch kit and installed it over the weekend. It provides a very solid hitch installation.

Installation, following the CURT directions was straight forward and install time was about 3 hrs (working at a leisurely pace).

If you follow the provided directions step by step the work should go smoothly. I backed the rear of the car up on some (~8") ramps to provide some extra clearance - and really had no trouble accessing the various areas, once (as the instructions require) the tailpipe (which actually has 2 rubber hangers, rather than 1 as indicated on the directions) and DEF tank are lowered.

Make sure you have all the tools outlined in the instructions (eg Metric sockets etc). I used a pair of aviation snips to trim the exhaust heat shield - it's aluminium and cut easily enough.

Check and count the nuts/bolts in the bag, since my kit was short 2 of the (#HFN 1213) flange nuts - so I had to substitute a couple of smaller nuts/bolts from my junk drawer until I get to the local hardware store today. No need to use the hitch in the meantime.
The temporary nuts/bolts are for connecting the under-car bracket to under the rear hitch area so it will be easy to replace then with the proper nuts/bolts...

Next project is figuring out and installing the wiring harness for the trailer lights. I'm planning on going with a Reese 78104 which provides for separate wiring for tail lights, brake lights and left and right turn signals - and according to the packaging "Draws power directly form the tow vehicle battery; uses less than 5 mA of the vehicle circuit" (ie. shouldn't interfere with ML350's existing lighting) and includes "Upgraded circuitry works with vehicles that use pulse width modulation (PWM); this gives the trailer lights full brightness."

Will let you know how that goes...

Cheers, G

stas2007

Very cool,
I just received all my parts today and will be installing next couple of days,
did you have to trim any of the plastic on the rear bumper, or just the heat shields?

UberFusion

Good luck on your install...

Wondered the same thing myself as I got started - but no, the hitch mounts up very tightly to the black fascia, so no trimming needed - and in fact you wind up pushing 2 (supplied) plastic 'peg' fasteners up through the existing tabs on the fascia into the hitch frame to secure the fascia.

Let me know how you make out on the wiring connection - key step seems to be getting access to the rear lights. On my vehicle on the driver's side you can open up a hatch panel (covers speaker) and see some of the tail light wiring and on the other side there is also a panel that allows some access to the car wiring...

Thinking out loud ... I would guess since the passenger side seems to have better access to the wiring I'll plan on mainly working from this side - ie. after figuring out which wire is which going to the rear lights, I'll connect a) the 12 VDC feed heavy red wire to the near by "cigarette lighter" outlet (assuming it is "always on" (need to check - otherwise up to the battery), b) the brown wire to the tail light wiring, c) the green wire to the right turn light, d) the red wire to the stop light circuit and e) run an extended wire over to the other side of the car to the left turn signal wire...

Hope that will work...

Await progress updates and any suggestions from you...

All the best, G

UberFusion

OK - got the trailer lights module wired in! - and working.

Pretty straight forward using the above mentioned module.

I worked from the right (passenger) side, through the access panel in the 'trunk' near the tail lights. From there I was able to get at the rear light wiring - ie. there is a white plastic connector at the back of the tail lights that connects the car's wiring harness to the tail lights. By pressing on the small tab you can remove the connector and get better access to the wires.

For my vehicle (on the passenger side) the wires were as follows;
- Brown = Ground
- Blue = Tail lights
- Green = Stop lights
- Purple = Right turn signal

I connected the trailer wiring module wires correspondingly to each of these wires, connected the white ground wire from module to an existing near by ground lug bolt and tapped into the 12 VDC wire that went to the nearby 'cigarette lighter' plug for the 12 volt power feed (heavy red wire) to the module.

Note: the 12 volt power to the cig lighter plug is only on when the car is running so really it's not the best place to hook up the power for the module, since the trailer lights won't be on unless the car is running - but I went this way (temporarily) just to get the trailer wiring tested and working and I'll go back in and run a new wire from the module to the battery + terminal.

For the left side turn signal I ran a wire from the module back across the trunk - ie. in behind the liner for the spare tire, up under the plastic moulding that covers the trunk door latch and then again in behind the spare tire liner and up into near the wiring for the left tail lights.

Similar to the right side, there is the same white plastic wiring connector that plugs into the tail light assembly. Remove it by pressing the tab to get better access for connecting to the turn signal wire. As I remember the left turn signal wire is a dark (black?) wire, and again going by memory it is the 2nd wire; the first being the ground wire. To be sure in any case check out the exact wires to make sure you use the proper wire.

Working slow and steady with a few breaks, it took me about 2 hours to do the above.

edgilmer

I bought and installed the Curt Trailer hitch a week ago and noticed it is significantly lower than a factory hitch. Does anyone else who installed the Curt Hitch notice the same thing? Any easy solutions other than a hitch adapter to raise it?

Thanks!

UberFusion

I noticed the same thing. It wasn't 'unusably' low but I wanted it a bit higher so to overcome it I reversed the ball on the 'tongue' bar that slides into the hitch frame...
The end of the tongue that holds the ball is curved so when you turn it upside down and then mount the ball on the top it raises the effective height to a near perfect level - worked for me any ways...

Mark Ilacqua

Have you had any issues with the wire harness install?

UberFusion

Have had no problems with the wiring harness - works great.

Mark Ilacqua

Great, thanks. My friend who is a mechanic will give it a try.