Towing Adapter for Mercedes GL450

[ReikiRocket]

I purchased a 2011 Mercedes GL450 to tow my 1974 Airstream. The guy who sold me the Airstream included the hitch and pigtail and I swear I remember the Airstream’s brake and signal lights were working when he delivered it with his pickup truck.

When we went to connect the trailer to my car using the provided pigtail, it didn’t work. We were getting electricity readings, but couldn’t figure it out and worried maybe we cut some crucial wires on accident. The dealer said it’s just because we have a non American car and we need an “adapter” which should solve the problem.

My new problem is when I search for an adapter online, so many different types of products pop up and I don’t know what to buy. Some products look like an entirely new pigtail. Anyone have any idea as to EXACTLY the search terms I should be typing in? Or better yet, a link to the product I need?

[Prettygood]

That was a lazy answer from the dealer. If it is a seven pin, it should work.

Check to ensure that all required fuses and relays are installed in the 450. You may have the wiring, but not the fuses installed in the box. I found a similar issue while towing with my dad’s F-150. Wouldn’t be surprised if it was a similar issue. Good luck

[gator.bigfoot]

Check to make sure the trailer hasn't been updated to led lights. This won't work with the stock setup. If you don't have led lights then make sure the trailer plug configuration is the same as your TV. There are numerous threads on the subject on this forum.

[ReikiRocket]

Good point! I don’t know enough even to be dangerous. All I know is that the headlights work just not the brake or signals.

[ReikiRocket]

The trailer definitely doesn’t (didn’t) have LED lights. I don’t have a TV in there (I gutted it for a mobile business) to compare anything against.

[Belegedhel]

There are at least three potential issues:

1) Trailers in the 70's were not wired to today's standards. You will need to figure out if your trailer still has the original configuration or if the prior owner rearranged to to match today's standards. He may have left the wiring configuration in the trailer alone, and just fiddled with the umbilical to achieve an "old-to-new" adapter. If you don't have that umbilical and are trying to use a brand new "standard" umbilical, it wouldn't work in this case. There are several threads on these forums discussing how to correct the non-standard wiring.

2) The Mercedes needs to see a certain amount of resistance on the lines to convince it that you have a trailer in tow. If your trailer has LED tail lights, then you won't have enough resistance. So your choices are to either put an in-line resistor in the trailer, or to use a 7 pin adapter with the resistors built in--this is probably what the dealer was refering to. I believe eTrailer.com has some products/information to help with this one.

3) My 2008 GL came without a reciever. I installed the factory receiver and factory wiring, which plugs into an electoric module (SAM REAR), which does all the thinking about whether you are towing or not. The tutorial I followed (I think from the MBWorld forums), suggested that "SAM Rear" module may need to be replaced. I ended up replacing mine because the dealer was of zero assistance getting the thing set up. I think my real issue was #2 above, and the SAM module was fine. Link to that tutorial is below:

https://mbworld.org/forums/gl-class-...llation-2.html

good luck!

[ReikiRocket]

Thank you for your detailed response Belegedhel.

All the previous owner let me know was that he made a new pigtail (not sure how one “makes” a pigtail, but that’s what his text message says) and did nothing to rearrange the connections, which is what I assume is the same thing as having left the wiring configuration in the trailer alone. I’m using the pigtail cord (is that the same thing as umbilical) that he gave me and worked for him on his truck. The current pigtail is a 7-pin plug, which is what my Mercedes has on it, too. If I’m understanding correctly, it may just need a different pigtail (umbilical) than the one he gave me to include an “inline resistor?”

[gator.bigfoot]

TV = tow vehicle

[Belegedhel]

Originally Posted by ReikiRocket

Thank you for your detailed response Belegedhel.

All the previous owner let me know was that he made a new pigtail (not sure how one “makes” a pigtail, but that’s what his text message says) and did nothing to rearrange the connections, which is what I assume is the same thing as having left the wiring configuration in the trailer alone. I’m using the pigtail cord (is that the same thing as umbilical) that he gave me and worked for him on his truck. The current pigtail is a 7-pin plug, which is what my Mercedes has on it, too. If I’m understanding correctly, it may just need a different pigtail (umbilical) than the one he gave me to include an “inline resistor?”

If you have the pigtail that the previous owner used, then it is inconclusive whether issue #1 is solved via reconfiguration of the trailer, or adaption created by the pigtail, but, it should not be the reason your lights don't work. So I wouls say, move on to issues #2 and #3. Start by finding out whether the tail lights have been retrofitted with LED lights or not. This will let you know if installing an in-line resistor or using an adapter is the thing that is needed.

good luck!

[ReikiRocket]

Originally Posted by gator.bigfoot

TV = tow vehicle

I feel dumb!

[ddhisself]

The first thing I would recommend is that you make certain your Airstream is wired to the industry standard. The simplest way to check that, would be to have a friend hook up the umbilical to his TV that you know is functioning properly. Assuming that trailer wiring is correct, I have had several customers with late model European vehicles (I am a U-haul dealer), whose vehicles checked out well with a test light, but would not make trailer lights work. I discovered that an adapter is necessary for those vehicles. It is called a 'trailer connector with lamp out bypass 7-way RV to (in your case) 7-way RV-vehicle end 20142" from e-trailer. I currently inventory a seven way to 4 way flat European adapter for these particular vehicles so they can tow U-haul type trailers. U-haul trailers have either LED lamps or regular bulb lamps, and with the adapter the European vehicles can make either system function.

[slpiotro]

I have had three ML 350's and one trailer (2007). The first one (2008) needed the pigtail adapter, the second (2011 late year or early 2012) didn't and the current one 2014 doesn't. (In case anyone is wondering, great lease deals on the first two, bought the last one and plan on keeping for a long time.)
So somewhere between the 2008 and 2012 year, they solved the reading the pigtail signals problem. I would try the adapter (they are not expensive- comparatively) and see. If the lights worked on the truck that brought it over, the European vehicle issue of reading the signal is the likely culprit. Just my guess.

[ReikiRocket]

Originally Posted by slpiotro

I have had three ML 350's and one trailer (2007). The first one (2008) needed the pigtail adapter, the second (2011 late year or early 2012) didn't and the current one 2014 doesn't. (In case anyone is wondering, great lease deals on the first two, bought the last one and plan on keeping for a long time.)
So somewhere between the 2008 and 2012 year, they solved the reading the pigtail signals problem. I would try the adapter (they are not expensive- comparatively) and see. If the lights worked on the truck that brought it over, the European vehicle issue of reading the signal is the likely culprit. Just my guess.

OK, so all signs are pointing to this LED adapter (even though the trailer doesn't have LED lights). Mercedes is convinced that's the solution and were nice enough to print out a page from eTrailer's website to get the adapter. I called eTrailer to buy the adapter and they told me to basically slow my roll and that if I put the adapter on my car, it'll blow fuses. Now I'm scared as hell to try the adapter.

In your situation with the 2008, I assume your trailer did NOT have LED lights, but the LED adapter was the solution? And it didn't blow any fuses?

[ReikiRocket]

Called Mercedes again. He explained that the monitoring system gets confused and even if the adapter blows the fuse, the fuse is a simple and cheap fix. Gonna try the LED adapter. Fingers crossed!

[Belegedhel]

My trailer definitely does have LED tail lights that I retrofitted into the 1970's housing myself. I do have a second set of conventional (non-LED) towing lights with a flat, 4 prong connection, that I used with my GL and a 7 pin to 4 pin adapter, and these worked fine, so I was convinced the issue was with the resistance (or lack thereof) in the Airstream. Rather than use an adapter, I just installed in-line resistors inside the trailer.

I don't see why the adapter would result in blown fuses. It should be putting a resistance of about the same value as a conventional tail-light bulb, nothing more dramatic than that. For that matter, I do have an adapter that goes from 7 pin to 4 pin and has the resistors built into it, for when I rent a utility trailer with LED lights on it. It has never resulted in any blown fuses or other issues.
I have used it with trailer that do not have LED lights as well (in which case you would think the GL would be seeing double the expected resistance), and no problems there either.

good luck!

[gator.bigfoot]

I just added non led lights to the umbilical connection point on the inside of the trailer as a lot of others have. This added the missing resistance and solved the issue with the TV.

When I had an issue in regard to my TV I just made a connector to plug into the back of the TV without the trailer. It has the lights and an halogen bulb hooked up to the brake controller. Now I can see in a hurry if all is functioning. The cable is long enough that I don't have to get out of my car. I can activate the lights and the brake controller and see that the TV is fine.

[Tom_T]

Originally Posted by ReikiRocket

I purchased a 2011 Mercedes GL450 to tow my 1974 Airstream. The guy who sold me the Airstream included the hitch and pigtail and I swear I remember the Airstream’s brake and signal lights were working when he delivered it with his pickup truck.

When we went to connect the trailer to my car using the provided pigtail, it didn’t work. We were getting electricity readings, but couldn’t figure it out and worried maybe we cut some crucial wires on accident. The dealer said it’s just because we have a non American car and we need an “adapter” which should solve the problem.

My new problem is when I search for an adapter online, so many different types of products pop up and I don’t know what to buy. Some products look like an entirely new pigtail. Anyone have any idea as to EXACTLY the search terms I should be typing in? Or better yet, a link to the product I need?

The Euro SUVs sometimes need the adapter to bypass the test circuit function, including Audi, BMW, MBZ, VW & Porsche Cayenne/Macan SUVs.



This has issue been discussed at the big topic on AirForums for the Euro & Alt-to-USA TVs, as well as a bunch of other really good stuff for Euro SUV owners, at the link below...



http://www.airforums.com/forums/f463...rs-134917.html



The Curt/Tow Ready adapter which was recommended to me from that topic is the one at the link below, & I know that it has worked for other Audi Q7/Cayenne/VW Taureg owners, as well as at least one (or more) MBZ GL 450 or 550 owner.



You can check around for best price on this item at the link below ....



https://www.etrailer.com/Wiring/Tow-Ready/20142.html



This should work for your GL450 + trailer.



And for the Ford truck owners or potential buyers out there - be aware that Ford has done something to screw up their software on the 2018> F150/250/etc. trucks which won't work the trailer lights on our 1960 Avion - even with this adapter!


Pre-2018 Fords were fine & never needed the adapter, Dodge/RAM of all years still works fine - since I can plug the trailer into another vehicle parked next to the 2018 Ford F250s which we rented & it works, but not in the Ford for 7 different 2018 F250s on 5 separate rentals in 2018.



I don't know if this Ford hook-up issue is with newer trailers, but it's BS that Ford cannot figure out the problem & simply denies it. So we rent the RAM 2500 from Enterprise Truck Rental now, & Ford is also losing other buy, lease & rental business on this problem.


Cheers & Happy Holidays!
Tom
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[ReikiRocket]

Originally Posted by Tom_T

The Euro SUVs sometimes need the adapter to bypass the test circuit function, including Audi, BMW, MBZ, VW & Porsche Cayenne/Macan SUVs.



This has issue been discussed at the big topic on AirForums for the Euro & Alt-to-USA TVs, as well as a bunch of other really good stuff for Euro SUV owners, at the link below...



http://www.airforums.com/forums/f463...rs-134917.html



The Curt/Tow Ready adapter which was recommended to me from that topic is the one at the link below, & I know that it has worked for other Audi Q7/Cayenne/VW Taureg owners, as well as at least one (or more) MBZ GL 450 or 550 owner.



You can check around for best price on this item at the link below ....



https://www.etrailer.com/Wiring/Tow-Ready/20142.html



This should work for your GL450 + trailer.


///////

Tom, thank you so much!!!!