Trailer OEM Module Questions

aradsma

New member
Hello, I just got a 2007 Sprinter that appears to have the factory OEM module. I have tried to get it to work on a number of trailers, but every trailer gives me a different outcome. I have tried 3 different 7-way to 4-flat adapters on each, with the same results:

Trailer 1 (6x12 enclosed -regular bulbs): Brake works, left and right signals flash normal, but no running lights
Trailer 2 (5x10 open-regular bulbs): Brake works, left and right signals flash normal; no running lights, but right running lights flash same as the right turn signal
Trailers 3,4,5,6 (boat trailers, some with LED lights, most with regular bulbs): Didn't have someone to check brakes, left and right signals do a rapid flash (one super-quick flash every time the turn signal turns on), no running lights

I have measured with a voltmeter (with trailers connected) and never get any voltage out of the running lights pin.

Any suggestions what I can do to resolve this?

If your recommendation is to change the trailer module, can anyone confirm where it is located? I have seen some documents that say it is in the rear of the vehicle, and others that show it is under the drivers seat (see attached image - is that the location of the module?)

I also have a 20A fuse in position 14 (manual - "Trailer Socket") and a 25A fuse in position 15 (manual - "Trailer Recognition Device"). Do either of those mean I have Trailer Stability Assist?

I know some of these questions have been asked before, but I have never seen a resolution. Is there a troubleshooting guide for OEM trailer wiring?
 

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mean_in_green

>2,000,000m in MB vans
I had a fault with rapid indicator flashing when trailer connected. Proved to the dealer with a lightboard that it wasn't my trailer. It was the trailer module, replaced three times under warranty. The current one is about three years old now so whatever the issue was appears to have been resolved.

The dealer admitted they couldn't explain it further. As I didn't do it myself I can't help with the location except to say I believe it's under the seat.

Ask for warranty consideration as there clearly was an issue.
 
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aradsma

New member
Thanks mean_in_green.

Anybody else have funny operation out of the module? I found the part for $250 online - it would be nice to be a bit more sure that it is the module before spending the $$ on the part!
 

sailquik

Well-known member
aradsma,
What makes you think you have the factory trailer towing package?
Is your receiver hitch cross member made by ORIS? Does it have a MB part number on it?
You do not have the OEM trailer assist feature....that wasn't added to NCV3's until 2010 or 2011.
Have you unplugged the connector on the back of the 7 way plug to test each wire coming from the
front of the van?
Having 3 different results from 3 different trailers sounds to me more like a trailer issue than a problem with
the Sprinter wiring.
Which pins in the 7 pin round connector in the back of the Sprinter give you voltage.
If I recall correctly the pin outs for the 7 way are molded into the cover for the female receptacle on
the back of the Sprinter.
You should be able to get Right turn....left turn and running lights + a ground out of your 4 way adapter.
Have you tried a different 4 way adapter?
There may be a "diode block" back in one of the rear quarter panels (this is sounding more like a T1N than
an NCV3) and diodes do go bad.
Follow the harness back from the plug on the rear of the 7 way and see if it goes into the body on the LH side.
If not, you probably have the NCV3 trailer wiring harness and the modules are up in the drivers seat box, but the
trailer module is usually the one up on the cross bar at the top of the box.
Hope this helps,
Roger
P.S. Send me a return email address and your VIN # by PM (up at the RH top of the page) and I can pull your data card
and confirm that your Sprinter had the factory installed towing package..
 
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aradsma

New member
Hello,

The hitch is the factory ORIS hitch, and has a bunch of german on the labels. I also have that module I circled underneath my seat, and the two fuses for the towing system, so I am quite sure that it is the 2007 NCV3 factory hitch setup I have.

I tried 3 different 7-round to 4-flat adapters, all with the same results. I also know that all these trailers work on 3 other vehicles, so I am quite certain that it is not the trailers.

If I measure the output on the 7-round connector with no trailer attached, I get 12V everywhere - I believe this is part of the trailer sensing circuitry. If I measure with a trailer attached (made an adapter that I can measure the voltage while a trailer is attached) I get normal type readings on the left/right turn signals, but it is really hard to tell with a volt meter since the lights are flashing... It reads 11V then low (~1V) and jumps around as they flash. There is no voltage on the running lights. The pin outs on the 7 way are molded into the cover - kind of handy for troubleshooting if you could only measure those with no trailer attached!
 

sailquik

Well-known member
Adam,
Do you have the 4 little round parking sensors in the rear bumper of your Sprinter?
I think that is really what the "trailer sensing" module is all about.
If you put a trailer on the back of a Sprinter with the rear bumper sensors, the Sprinter's
systems have to be able to "sense" that it's there, which happens when you attach the trailer connector.
My guess would be that you might need to take your Sprinter to a dealer with the MB SDS diagnostic system and have
them check out the trailer sensing module.
Also sounds like you don't have a good ground pin in your 7 way. Might want to check the ground pin to the chassis of
your Sprinter. Should be 0.00 ohms (or very close to zero).
The fact that your turn signals go from 11 vdc to 1 vdc and back to 11 vdc indicates a possible grounding issue.
I just talked to someone very knowledgeable about this and it was suggested that the MB SDS can identify issues with these
modules.
Might cost for the diagnostics, but there may be no other way to ensure that the computers are playing nice with the trailer
wiring.
Just another thought, could you get a 7 way male connector and only hook up the wires you need, Brake lights/turn signals/running
and a good ground.
Also check the ground in your 4 way adapter (s) to the other 3 pins to ensure that it's completely isolated.
Hope this helps,
Roger
 

aradsma

New member
I don't have those sensors, so I don't think I have TSA, but somehow the electronics know when a trailer is attached. I have checked all grounds, and they are good. The changing voltages on the blinkers is normal too - it changes from 0v to 12v when it turns on the light for a second, the driver back to 0...my meter just can't keep up.

As for going to Mb, I get a sense that it would make more sense to just order the part. If it doesn't work, I can sell it again, but if it does, then I didn't pay Mb $250 to tell me I needed to buy a $250 part. I am scared of going in there and paying their service rates, especially if it is a phantom type problem that takes hours to diagnose.

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mean_in_green

>2,000,000m in MB vans
I have Trailer Stability Assist. No rear parking sensors though, just the act of connecting the trailer plug enables the enhanced ESP.

Only felt it in action once, not going particularly fast but on trailing throttle downhill in a tightish bend. ABS pump had a mild workout.
 

Motovan

New member
This happened to me too and it was perplexing to me and my dealer. I had a 5x7 haul mark with incandescent lights where the flashers and brakes worked but the running lights would only flash for a sec when hooked up. I fixed the issue by replacing some of my incandescent bulbs with led's. I think the output on the sprinter trailer harness is very weak. Try hooking up your trailer and unplugging one bulb at a time until the running lights pop on.
 

Trayscott

New member
Roger, I need trailer wiring and preferably a Oris hitch. Your thoughts. Not ideal but a new sprinter is not happening. I understand the issue with aftermarket while keeping the step but is the aftermarket hitch mounted similarly to the factory hitch. Appreciate your input on the forum
 

sailquik

Well-known member
Trayscott,
T1N or NCV3?
I had the eTrailer/Curt aftermarket hitch on my '06 T1N 3500, and while it did the job, the fit and finish left a lot to be desired.
So, if you have an NCV3 and want to add an Oris cross member/receiver I'd look in Sprinter wrecking yards/breakers for a used one.
As far as the wiring, you might also find that in a wrecking yard/breakers and be able to take all the wiring, the 7 way on the back and
the modules under the driver seat and transfer it to your Sprinter.
You will in almost any case have to visit a Mercedes Benz Sprinter shop and have your programming updated to include the trailer towing
pkg.
If you have an earlier NCV3 ('07-'09 Dodge Freightliner) you may be able to purchase the trailer harness new from one of the MOPAR outlets.
I honestly think that you can have your rear step, just need to modify it a bit to fit around the ORIS crossmember.
They mount in the same holes. Might have to notch a bit, bend/weld a little offset in the step mounts, but it's very possibly doable.
Below is a photo of a brand new 2014 3500 Cab/Chassis that shows the 4 holes (reinforced with tubes through them) that are engineered
into the rear of all Sprinter chassis (Cargo/Crew/Passenger/Cab-Chassis) to accept the ORIS factory rear cross member/receiver.
 

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Trayscott

New member
2008 NCV3 long and tall. I understand the quality difference in hitches. I can paint till my hearts content. Biggest concern is how they mount. My plan was to install a step of some sort. Maybe a cool stainless or aluminum fabbed up by my brother. Don't like the aftermarket that puts the hitch point further rearward with factory step for obvious reasons posted a few weeks ago with the cracked unibody. Debating on a larger pop up or smaller hardside/hybrid camper so 4000 lbs max. Think my drivetrain is very healthy, 186000 but running like a champ, quiet, smooth and mpg where it should be from what I can tell. Now the harness is another story. The Freightliner dealer uses a hitch guy nearby for their dealer installed trailer equipment. Will get details before the are even considered an option. Thanks a bunch for your insite
 

ElWhoppo

New member
My experince with trailer modules was by trial and error. Mine is from Drawtite. Hitch fit perfectly to frame rail after discarding tie down brackets. First module didn't work, power from the tail lights is insufficent to power a trailer. The module for combineing brake and blinker functions w/o power assist from the battery did not work. MBs wireing and fuse relay too light to sustain the additional load and you get the warning blinking and relay overload. Proper module must have power assist from the battery. I ran a fused 12 guage wire from the battery to the cavity in the rear door jamb near the left tail light. The module uses the vans wireing as signals to switch on the proper lights but using the batteries power. Visualize this as a solid state relay. I ran into similar problem with the reverse wireing when attempting to install a backup camera. As for where your module is follow the wireing from the trailer plug back. Hope this helps.
 
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Trayscott

New member
My experince with trailer modules was by trial and error. Mine is from Drawtite. Hitch fit perfectly to frame rail after discarding tie down brackets. First module didn't work, power from the tail lights is insufficent to power a trailer. The module for combineing brake and blinker functions w/o power assist from the battery did not work. MBs wireing and fuse relay too light to sustain the additional load and you get the warning blinking and relay overload. Proper module must have power assist from the battery. I ran a fused 12 guage wire from the battery to the cavity in the rear door jamb near the left tail light. The module uses the vans wireing as signals to switch on the proper lights but using the batteries power. Visualize this as a solid state relay. I ran into similar problem with the reverse wireing when attempting to install a backup camera. As for where your module is follow the wireing from the trailer plug back. Hope this helps.
Whose module did you end up using, Scott
 

aradsma

New member
Maybe I should put the question out there like this:
Does anyone have a factory module/wiring setup in an 07/08 that actually works on all trailers? Does everyone need to rig something up to make the trailer lights work? If so, is there a way to simply use a relay to power the running lights that is turned on by the factory running light wire?

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Trayscott

New member
I have yet to look but big blue bus on here mentioned something about this. I bought wheels from him last summer and I was really new to the sprinter stuff so it didn't seem to mean much at the time. I will look too. He tows a decent size boat with his modded 2007
 

aradsma

New member
So I hooked up a small trailer, with not many lights, and started popping off the running lights. No difference... the running lights never turned on.
 

ElWhoppo

New member
This might not be where you want to go but I know it will work. At site Towready.com look for ModuLite HD Protector. This is the second module I installed after the one w/o the power from the battery did not work. See earlier post. A Drawtite dealer supplied mine, ~$60. Solved all my problems. If running a wire to the battery is a problem, there are two cig 12v outlet on my rear door posts. This may surfice for power. It is already fused and being what it is (resistent heating) should carry the load.
 

cfrick

New member
I was having the same issue with no parking lights on a 20' Wells Cargo box trailer. When connecting the trailer the running lights would flash 2/3 times then stay off. What caused the problem I believe was the interior lights in the trailer. If I turned them off it would operate properly. I believe all the lights in combination are too much of a draw for the module. Perhaps swapping a few bulbs for LEDs as suggested will help.
 

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