Trailer Wiring OEM Harness vs Aftermarket Light Module

[220629]

Skip down a bit in this post for T1N parts info. Near the end is a plug and play NCV3 option. That NCV3 option does not allow TSP safety system activation.

OK people it's time for me to confess that I (yet again?) put out some misinformation on a forum. I have admitted to being a parrot other times. This time I added to the info to the point of being way wrong.

One of the posts is here:
https://sprinter-source.com/forums/showpost.php?p=53264&postcount=4
*******

Mike,
Glad I could help. Not that you asked, but to expand a bit. The OEM harness doesn't just take care of the lights, it also lets the computer know that there is a trailer being towed. That affects the way the computer reacts to a skid situation. Because I tow only about 3000# and towing is relatively infrequent I decided that the installation time and cost was not worth the OEM for my situation. By using a trailer light module as I have one ends up towing without the computer control ESP and ASR aware of the trailer being there. If you plan to tow more weight than I do, or plan to tow a majority of the time I think the OEM harness and included computer control is worth considering. It is a bit pricey and much more involved to install.

If you do go with the aftermarket module you may want to consider what I installed. When I ran the dedicated 12 volt power back to the left rear of my van I used a larger feed wire. I fused it at 30 amps at the battery (I think...maybe 40. It's a big cable that was already there for a handicap lift) and then split it off to 2ea. fused 20 amp circuits in the area above the rear light pod. One 20 amp went to the trailer module. The other 20 amp went to an accessory (cigar lighter) receptacle for camping use. It has often been convenient to have that 12 power available in the back of the van.

Hope this does some good. AP

*******
The bold text above sounds pretty good doesn't it? Except that it's completely wrong [For NAS aka NAFTA Sprinters prior to 2010 MY], it would be great.

After posting my "ESP, ASR OEM Trailer Harness Wiring" question and not getting any definitive answers
That post is here:
https://sprinter-source.com/forums/showthread.php?t=6918

I decided to stop being so lazy and follow up with Dodge. I sent an e-mail to them 7/12/09 basically asking whether the Sprinters with OEM trailer harness interfaced with the ESP®/ASR or had TSA trailer stability assist. If they did, what years were included.

After a few e-mails and phone conversations I finally got my answer from Dodge today in a voice message. TSA has not been available for NAFTA Sprinters to date. It is expected in model year 2010. There is no interface with the ESP®/ASR by using the OEM harness.

Given the fact that there is no interface with the computer controls I personally find it difficult to justify the expense, installation effort, and complexity of the OEM trailer light harness over a properly selected aftermarket trailer light module which uses low current trigger signals and a dedicated 12 volt source. All the OEM harness does is make the trailer lights work, as does a light module.

My sincere apologies for helping to lead anyone down the wrong path. Hope this does some good. vic

2011/08/18 edit: Wire colors from my 2004 which should be standard for all NAFTA T1N's can be found here. Go to post #4.
https://sprinter-source.com/forums/showthread.php?t=3301

TSP and 2010 MY
As of NAFTA model year 2010 the TSP feature is available on our Sprinters. That is an excellent reason to use the OEM harness. An aftermarket trailer light module and brake controller will not allow activation of the TSP feature. That said, the TSP is not available in earlier models so I feel a powered aftermarket module may be a good choice for some people. Altered Sprinter provides good information about TSP in post #20.

Any Euro model Sprinter owners reading this thread can ignore the electric brake information as I'm told they are not applicable.

*******************************

20170809 Edit: Members often ask what parts to buy.

T1N or NCV3 (Traditional wire tap module.)

I mounted this to the under panel just aft of the T1N spare tire.
Tekonsha 119147 ModuLite HD Protector Trailer Light Power Module
https://www.amazon.com/gp/product/B00ASY29C0/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1

T1N or NCV3

I used ss hose clamps to strap this to the hitch structure.
Hopkins 47185 Multi-Tow Adapter
https://www.amazon.com/gp/product/B0002Q80GS/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1

T1N or NCV3 (Basic brake controller.)

Older model timed brake module. (Fine for small(er) trailers. Ignore "Does not fit".)
Reese Towpower (74642) Brakeman Timed Compact Brake Control
https://www.amazon.com/gp/product/B0016KA9PY/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1

T1N or NCV3 (Proportional brake controller.)

Some (eg. - Sailquik Roger) prefers and recommends a more modern proportional brake controller. It is the better choice overall if cost is not an issue.
https://www.amazon.com/s/ref=nb_sb_...rh=n:15684181,k:proportional+brake+controller

T1N Trailer Hitch
Fits a 2500 140 WB T1N with either the step bumper or standard bumper.
Reese 33089 Class III Custom-Fit Hitch with 2" Square Receiver opening, includes Hitch Plug Cover
https://www.amazon.com/gp/product/B000RNW5PI/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

Added:


********************************
Some comments OEM Added Harness vs Aftermarket Module
(Admittedly somewhat biased.)

Aftermarket Powered Module
Pros:
Readily available.
Less expensive.
Easier installation.
No relays in body panels to get wet and fail.
Cons:
It's not OEM.
Won't enable TSP trailer safety.

Added OEM Trailer Light Harness/package
Pros:
It's OEM
It *may* play better with parktronic, etc.
Cons:
Can be difficult to source.
More expensive.
Needs to be dealership programmed.
More difficult installation.
Doesn't play well with LED trailer lights.
Won't enable NCV3 - 906 TSP trailer safety (unless exclusively installed at the factory. 2016?+ can now have TSP added by a dealership).
Has relays and wiring in body cavity that get wet and fail.

My recollection is that the T1N OEM suffers the wet relay problem. I didn't dig up any posts. Here's some NCV3 comments related to wet relays and failure.

Brian, we were informed by our neighbor last night that one of our tail lights was on. I went to check it out and sure enough the left light was on, so I disconnected the batter, TA DAAA the light and everything else went dark. Connected the battery again and the light came back on, disconnected the battery again and went inside. Today I checked this great site and found your message. Went to our 2007 NCV3, found the 3" plug and pulled the DRIPPING wire harness out. I then found the drain hole and got out of the way of the steady stream of water. I connected the battery again and found one of the relays was warm, not hot AND the light did not come on unless directed by the light switch. Thank you so much for your message!

Funny thing is, same thing happened to me. First, I noticed that you have an aftermarket towing hitch and harness. Is that correct? If so, try to disconnect your towing wiring harness from your main battery.
Dodge towing wiring harnesses consist of six relays. They are located below the tail light on the driver's side. When I opened mine, three of the relays were corroded and wet, but I only had to replace one. Check yours for any corrosion and if neccessary, change the relay. I got mine from the Dodge parts department at the dealership. To prevent it from happening again, make sure you move the relays up and isolate them so they don't get wet.
Hope this helped!

****************************
ADDED.
In newer NCV3's apparently Mercedes saw the light and moved the relays to under the seat. Roger revealed the change.

Guys,
I think you are mixing T1N (Dodge or Freightliner) 2002-2006 and early NCV3 (Dodge/Freightliner 2007-2009) with >2010 Mercedes Benz/Freightliner NCV3 trailer tow harness's.
There are no relays anywhere near the back of a 2012 NCV3.
All the relays and towing modules (TSA/Trailer Brake Controller) are under the driver's seat.
They are most often located on an upper module mounting bar above the normal electronics
found in Sprinters without the towing harness.
Roger

*******************

Added:
FOR NCV3 Sprinters.

Apparently eTrailer now offers a plug and play trailer light powered module which connects into the tail lamp assemblies.
Thanks goes to Kevsuda.

I ordered this one last week. https://www.etrailer.com/Custom-Fit...Sprinter/2011/118650.html?vehicleid=201151735

Your model year (2007 - 2013) can be entered. (As of Dec. 2017 a plug and play kit is not available for T1N's.)

2017 NCV3 is apparently available too.

https://www.etrailer.com/Custom-Fit...ter+2500/2017/118649.html?vehicleID=201751730

I’ve two buddies that use this system. It’s plug and play. Installs in a couple hours.

eTrailer shows how to use a simple lever and bathroom scale to measure tongue weight.
]

And other options. https://www.etrailer.com/faq-how-to-determine-trailer-tongue-weight.aspx

 

[sikwan]

Re: Trailer Wiring OEM Harness vs. Light Module

Don't worry Vic, you didn't lead me down that road. I just didn't believe it because of the limited 7 pin tow connector that doesn't provide any feedback from the trailer.

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

Don't worry Vic, you didn't lead me down that road. I just didn't believe it because of the limited 7 pin tow connector that doesn't provide any feedback from the trailer.

Sikwan,
I'm not so sure that other than a 7 pin standard trailer connector would be needed. The quote below is from this page:
http://www.whnet.com/4x4/towing.html

New M-Class (W164) with Trailer Stability Assist (TSA)
The factory-fitted package of measures will in future include the new Mercedes-Benz Trailer Stability Assist (TSA). This is an extra function incorporated into the ESP® Electronic Stability Program that is designed to offer drivers even greater safety when towing a trailer. TSA is capable of detecting the dreaded fishtailing motion swiftly and nipping it in the bud effectively. To do this, it uses the ESP® program's own sensory system and initiates precision brake applications at the front left and right wheels individually and alternately to stabilise the car/trailer outfit. TSA will be added to the specification of the M-Class from late August 2005.
from a Mercedes press release dated July 7, 2005.

Then again, I could be wrong. vic

 

[famof8]

Re: Trailer Wiring OEM Harness vs. Light Module

Thanks for the clarification AP!! The only reason to have the OEM harness would be to incorporate an electric brake controller at the front of the cab. A light converter will not support this application.

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

Thanks for the clarification AP!! The only reason to have the OEM harness would be to incorporate an electric brake controller at the front of the cab. A light converter will not support this application.

Famof8,
Thanks for the input.

That is an advantage, but you still need to add a trailer brake control unit because to the best of my knowledge it doesn't come with the OEM harness. Most likely the OEM connector under the steering column will need to be chopped off for a brake controller to be wired. To add a trailer brake controller with an aftermarket light module just requires wiring a 12 volt source, a wire back to the trailer connector, and a trigger signal from the brake switch. Basically some wire and connectors. It's a typical vehicle installation for a brake controller. Your point is a good one though I'm not at all convinced that feature makes the OEM worth the additional cost and effort for a DIY installation. YMMV.

20100627 Edit:
Some brake control generic info that may be useful:

Trailer Brake Controller Information (Proportional or delayed type)
http://www.etrailer.com/faq-brakecontroller.aspx

Typical Electric Brake Controller Wiring
http://www.championtrailers.com/Electric brake control wiring.pdf

A #10 AWG wire size (typically blue, but color isn't critical if labels or color tape marking is used) is a good idea from the brake control unit to the trailer connector to help avoid voltage drop. Especially when powering more than one axle of electric brakes.

vic

 

[bikergar]

Re: Trailer Wiring OEM Harness vs. Light Module

Vic

In your defense (not that you need it) I have read a statement in a 2008 Dodge Sprinter brochure that implies that something in the Sprinters thinking system is altered when you plug into the factory harness. It would appear that it was a misstatement by Dodge. I believe I still have the brochure, but don't have access to it at this moment. This will be a great test for my memory as I read it over a year and a half ago. OK, now where did I park my Sprinter.

Gary

 

[famof8]

Re: Trailer Wiring OEM Harness vs. Light Module

Vic:

I had to agree with your rationale for not purchasing the factory harness. After much research, I determined that your method was much simpler... and cheaper. I was even more convinced when I found that an online retailer (etrailer.com) preps the entire wiring packages for the standard 4-pin trailer lights (modulite) and the 7-pin connector necessary for larger trailers. The two kits were $85 total and include everything needed to complete the install, down to the crimp-on connectors, scotch locks, wire ties, circuit breakers and basic Sprinter wiring directions.

My install of a Curt Class III hitch, the modulite and brake controller wiring, as well as my existing Tekonsha Voyager brake controller should begin within the next week depending on the weather and delivery of the equipment. I will take pictures along the way to add to the info here on the site for anyone performing these steps in the future.

PS. I couldn't beat the prices... $169 for the hitch, $34.95 for the modulite package, and $49.50 for the 4-way / 7-way connector (with wiring package) that mounts to the hitch. Plus a 5% coupon on the entire order with free shipping!

 

[Sacto John]

Re: Trailer Wiring OEM Harness vs. Light Module

Thanks for clearing that up, I have been holding off buying the OEM harness based on expense alone. I have another question now, do I need a powered modulite or can I just tap and go with a un-powered converter? If I can get away with not running 12v back to the hitch it will make life much easier for me. The two trailers I have only have two rear lights and two marker lights and by etrailer.com calculations should not be drawing more than 8.4 amps, which the un-powered converter will handle. Is there anything in the Sprinters computer or monitoring system that will require me to run a powered modulite?

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

Thanks for clearing that up, I have been holding off buying the OEM harness based on expense alone. I have another question now, do I need a powered modulite or can I just tap and go with a un-powered converter? If I can get away with not running 12v back to the hitch it will make life much easier for me. The two trailers I have only have two rear lights and two marker lights and by etrailer.com calculations should not be drawing more than 8.4 amps, which the un-powered converter will handle. Is there anything in the Sprinters computer or monitoring system that will require me to run a powered modulite?

Sacto John,
I don't know the answers to your specific questions. I do know that the total current is not the only issue. Because the Sprinter computer is aware of the lights and monitors them, it perceives there is a problem any time the actual current draw is not within the programmed parameters. I would only recommend a powered module because I know for certain that will keep the thieving trigger currents low enough to keep your Sprinter computer happy.

That said, I am basing this on limited experience and knowledge which does not include multiple Sprinter trailer light module installations. Hope this does some good. AP/vic

 

[famof8]

Re: Trailer Wiring OEM Harness vs. Light Module

Thanks for clearing that up, I have been holding off buying the OEM harness based on expense alone. I have another question now, do I need a powered modulite or can I just tap and go with a un-powered converter? If I can get away with not running 12v back to the hitch it will make life much easier for me. The two trailers I have only have two rear lights and two marker lights and by etrailer.com calculations should not be drawing more than 8.4 amps, which the un-powered converter will handle. Is there anything in the Sprinters computer or monitoring system that will require me to run a powered modulite?

eTrailers.com recommended the unpowered modulite for the Sprinter. I even spoke with their customer service department to question their recommendation. After I ordered it, I did some more research and found that Hopkins also recommended the unpowered modulite. I spoke with Hopkins Technical Support and they insisted that the engineers don't mess around and if they recommend it, then it is good.

That being said... the Mopar harness for the Sprinter has a powered Draw-Tite modulite included within the harness. My thoughts are that if Chrysler has it, so should I. As a result, I dispatched my wonderful wife to the local NAPA that stocked the super-duper powered Hopkins modulite and installed it on mine today. I have real concerns that the unpowered modulite would cause ghosts in the electrical system, especially when I have seen bulbs with incorrect wattages drive mine batty. My other concern was that my trailer that I pull has 11 marker lights at just over .5A each and two tail lights at 2.2A each. That kind of draw on an unpowered unit sends shivers down me spine.

The short of my long story is it would probably work for a low draw application, but I personnally would not chance it. However, that being said, it just may work for your application and I do tend to respect Hopkins products. Let us know what you decide and how it works out. Good luck!

 

[Sacto John]

Re: Trailer Wiring OEM Harness vs. Light Module

Thanks AP and famof8, I am thinking on going with the un-powered modulite and see what happens, which leads me to my next question, if the computer has a problem with the extra draw how will I know?

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

John,
From what I've read on the various forums the trailer wiring issues with Sprinters can range from the computer simply thinking incorrectly that a light is out, all the way to the computer setting Limp Home Mode. If I recall correctly the LHM incidents are usually traced to shorts or grounds in the trailer related wiring. (Sometimes the vehicle harness, other times the trailer harness) I guess I would keep in the back of my mind that if you start having unexplained LHM episodes a first response might be to check the trailer wiring or disconnect the trailer light module.

Fortunately to date I have had no personal bad experiences to draw upon related to the trailer wiring or my powered module while pulling my trailer. Hope this does some good. AP/vic

 

[Sacto John]

Re: Trailer Wiring OEM Harness vs. Light Module

LHM would not be good...Decisions, decisions...

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

John,
If it helps your decision any, another advantage the powered module has is that it totally isolates your trailer lights from the vehicle wiring. The trigger signals cause the powered module to direct power to the trailer lights which is drawn from the dedicated trailer module 12 volt feed wire. If your trailer lights or trailer harness go bad (and that never happens on a boat trailer) it will blow the trailer module power fuse. Your Sprinter lights will 99.9% of the time remain unaffected. As the Sprinter lights sit relatively high a boat trailer often will not obscure the still working Sprinter lights. That's a pretty big plus for me. Sorry if I'm telling you what you already know. Hope this does some good. AP/vic

FWIW - I carry a set of magnetic trailer tail lights for emergencies. (We don't trust no stinkin' magnets. I'd still tie them on.) We often drive at night towing. I figured the 12 bucks on sale from Harbor Freight was worth the investment if the time comes that they're needed.

 

[Sacto John]

Re: Trailer Wiring OEM Harness vs. Light Module

Ok now I am going to ask for suggestions on what powered modulite to buy. Like AP I am frugal (some call me cheep), so the lower the price the better.

 

[famof8]

Re: Trailer Wiring OEM Harness vs. Light Module

Ok now I am going to ask for suggestions on what powered modulite to buy. Like AP I am frugal (some call me cheep), so the lower the price the better.

Frugal or cheap is not a bad thing. I would check the etrailer.com site under the electrical section. Make sure you select the powered modulite link. You can tell if the modulite is powered as it will have a lead marked "battery" on one side. They have been the lowest price in my search.

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

Below is a link to a thread that traced rear light problems to an OEM trailer harness issue. I think it's something to consider whether you're making the OEM vs aftermarket module decision, or deciding on how/where to route the OEM harness during installation. Thanks goes to Brian T for his follow up and pictures.

https://sprinter-source.com/forums/showthread.php?t=7505

AP/vic

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

Use a large gauge wire for your trailer brakes.

Sailquik has made many good suggestions on this forum and Yahoo sprintervan. I think this one is worth adding here.

"If you tow a larger trailer with electric brakes on more than one axle, I would recommend adding at least 1 #10 AWG blue wire to handle the additional current more brakes will need." Sailquik

20111217 edit: Electric brakes are used in NAFTA land. They are not used across the pond (Euro models).

The post is here:
Re: wiring for rear view back up camera and trailer hitch
https://sprinter-source.com/forums/showpost.php?p=92858&postcount=2

vic

 

[220629]

Re: Trailer Wiring OEM Harness vs. Light Module

A recent post in support of the OEM factory wiring harness. Nate claims the install took 2 1/2 hours. That's better than some of the dealer install times I've read about.
***
"I did get the wiring installed. It took me about 2 1/2 hours to get the factory harness installed.

What a great plug and play harness for the most part."
***
Thanks to Nate for the info.

Single post is here:

Re: Max Trailer Weight w/ Weight Distributing Hitch?
https://sprinter-source.com/forums/showpost.php?p=97729&postcount=26

As always with single posts the original thread can be accessed by using the link in the upper right corner.

vic

 

[Altered Sprinter]

Re: Trailer Wiring OEM Harness vs. Light Module

OK people it's time for me to confess that I (yet again?) put out some misinformation on a forum. I have admitted to being a parrot other times. This time I added to the info to the point of being way wrong.

One of the posts is here:
https://sprinter-source.com/forums/showpost.php?p=53264&postcount=4
*******
The text:
Mike,
Glad I could help. Not that you asked, but to expand a bit. The OEM harness doesn't just take care of the lights, it also lets the computer know that there is a trailer being towed. That affects the way the computer reacts to a skid situation. Because I tow only about 3000# and towing is relatively infrequent I decided that the installation time and cost was not worth the OEM for my situation. By using a trailer light module as I have one ends up towing without the computer control ESP and ASR aware of the trailer being there. If you plan to tow more weight than I do, or plan to tow a majority of the time I think the OEM harness and included computer control is worth considering. It is a bit pricey and much more involved to install.

If you do go with the module you may want to consider what I installed. When I ran the dedicated 12 volt power back to the left rear of my van I used a larger feed wire. I fused it at 30 amps at the battery (I think...maybe 40. It's a big cable that was already there for a handicap lift) and then split it off to 2ea. fused 20 amp circuits in the area above the rear light pod. One 20 amp went to the trailer module. The other 20 amp went to an accessory (cigar lighter) receptacle for camping use. It has often been convenient to have that 12 power available in the back of the van.

Hope this does some good. AP
*******
The bold text sounds pretty good doesn't it? Except that it's completely wrong, it would be great.

After posting my "ESP, ASR OEM Trailer Harness Wiring" question and not getting any definitive answers
That post is here:
https://sprinter-source.com/forums/showthread.php?t=6918

I decided to stop being so lazy and follow up with Dodge. I sent an e-mail to them 7/12/09 basically asking whether the Sprinters with OEM trailer harness interfaced with the ESP®/ASR or had TSA trailer stability assist. If they did, what years were included.

After a few e-mails and phone conversations I finally got my answer from Dodge today in a voice message. TSA has not been available for NAFTA Sprinters to date. It is expected in model year 2010. There is no interface with the ESP®/ASR by using the OEM harness.

Given the fact that there is no interface with the computer controls I personally find it difficult to justify the expense, installation effort, and complexity of the OEM trailer light harness over a properly selected aftermarket trailer light module which uses low current trigger signals and a dedicated 12 volt source. All the OEM harness does is make the trailer lights work, as does a light module.

My sincere apologies for helping to lead anyone down the wrong path. Hope this does some good. vic

Vic lets move this forward as to The latter 2010 Mercedes Sprinter with optioned ESP electronic Stabilization Programing.

ESP..Electronic Trailer stabilization
Briefly this was an exclusive Australian option for tins using an after market ABS ECU fully integrated trailer assist module adjusted via the DFV brake force distribution valve.
Mercedes Sprinter 2010
IF A CUSTOMER:Orders the trailer coupling or preparation for a trailer [OEM] ESP trailer stabilization is included as standard..Dealers should be aware of this option This additional function of the standard ESP is already uses the yaw sensor of ESP to recognize sinusoidal oscillations around the vertical axis of the vehicle,and initiates counteraction with active breaking intervention.
There are no additional sensors on the trailer coupling once the trailer begins to snake.ESP trailer stability brakes the front wheels to reduce engine torque !If several interventions are necessary the braking is reduced more severally;this unmistakeably makes the driver aware of the snaking trailer and that he is driving at critical speed to frequently.
The ESP warning light on the dashboard informs the driver that intervention is taking place.
Co-incidentally this can happen on a van without a trailer on board with steep mountain descents or inclines on sharp bends with multiple braking hence the option of fitting a telma retarder to assist in preventing excessive pressure and heat distribution on the vehicles brakes which may set up a limp type mode.

Note> this is a factory option.

such as this thread,as a possible example.
Engine Shutdown - ESP Problems
Richard
​