W164 Trailer Wiring Issue

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Wonky
Dernburg Wagon
Posts: 5
Joined: Fri 30 Jan, 2015 11:58 pm
Model you own: w164

W164 Trailer Wiring Issue

Post by Wonky » Sat 31 Jan, 2015 12:44 am

Hi guys. My first post on this forum but I am an admin on another car forum and regular poster on yet another (for my car).

A few months ago my daughter bought a used 2006 ML320 CDI Sports Luxury which has been exemplary so far. However, her main reason for purchasing it was to tow our horse float as we could no longer afford a 3rd car for occasional towing duties now we're retired. The car has what we believe to be a genuine MB towbar etc but when she hooked the float up none of the lights work. Worked fine on our previous tow car (Nissan Patrol) and when they wouldn't work we hooked it up to my SSV Commodore and it worked fine, so the problem is the car or car/float combination. The float was rewired and had LED lights fitted about a year ago and hasn't caused problems with any other cars.

We took it to our local elec auto guy (who does work for a number of local dealers so can't be too bad). Our daughter has a uni degree and is pretty good on car stuff but in the end she was confused about what he was telling her he thought the problem was. However, she thinks he was saying there was power to the trailer plug but he thought this MB (and other models?) had some sort of extra fancy electrical stuff and that maybe that had a fault.

Would someone be able to clarify or list some possibilities for me please because he was basically stumped without spending countless, possibly fruitless hours on it.

Thanks,
Gary

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Tony From West Oz
OZBENZ moderator
Posts: 3188
Joined: Mon 20 Jun, 2005 10:04 pm
Model you own: w202
Location: Bedfordale WA

Re: W164 Trailer Wiring Issue

Post by Tony From West Oz » Sat 31 Jan, 2015 2:10 am

Wonky,
Welcome to the OZBENZ Forum.
he was saying there was power to the trailer plug but he thought this MB (and other models?) had some sort of extra fancy electrical stuff and that maybe that had a fault.
Mercedes have lamp warning circuits which monitor the current on half of each lighting circuit and compare to the other half of the respective lighting circuit.

To prevent this system from incorrectly seeing a lamp out fault when a trailer is connected, the trailer lighting is supplied by relays, activated by the respective lighting circuit. As the relay draws only a small current compared with light globes, the system is not misled.

The trailer lighting adapter has a fuse which supplies power to the relays. If that fuse is blown, then you would not have any lights on the trailer working. This sounds likely to be the cause of your symptoms.

If there is power to the respective lighting circuits (at the trailer plug, with the trailer connected) then either the earth connection is gone or there is a fault on the trailer. The Earth connection via the plug is not essential as the chassis of the trailer makes reasonable electrical contact with the towing vehicle via the tow ball. The trailer lighting works with other vehicles, so it does not appear to be a trailer fault.

If he measured the voltage at the connector without any load on the lighting circuit, then there may be a faulty relay, but I doubt that all relays would be faulty ????

In my car, the trailer lighting adapter is located in the well behind the drivers side rear wheel, under the plastic lining.
You may need to research where the fuse for the adapter, and the adapter itself, in your daughter's car are located. Perhaps another member here can assist.

I am happy for others to chime in with their experiences and opinions, as my experienced with trailer lighting on Mercedes is limited to the vehicles in my signature lines below.

Regards,
Tony
Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

'83 W123 300D 325000km (Wife's car Josephine - sold).
'84 W123 300D replaced good OM617 912 with OM617 952 and enjoyed having good acceleration for the first time since first driving a 300D in 2002 - became engine and trans donor for 300CD Turbodiesel conversion. Now parted out.
'86 W124 300D sold (Wife's old car - sold )
'85 W123 300CD, 275 000km (Fatmobile) rebuilt turbodiesel from previous Fatmobile transplanted into 280CE (SOLD)
'99 W202 C250 Turbodiesel (my darling Wife's car - Sold)
'98 W202 C250 Turbodiesel (my car - Sold)
'06 Ssanyong Musso Crew Cab 2WD Ute (OM662 diesel and Auto Transmission)

Wonky
Dernburg Wagon
Posts: 5
Joined: Fri 30 Jan, 2015 11:58 pm
Model you own: w164

Re: W164 Trailer Wiring Issue

Post by Wonky » Mon 02 Feb, 2015 6:26 pm

Thank you for your reply Tony. Due to the fact I couldn't log on to this forum since I posted my question until now my daughter took it this morning to a place in Lynbrook that the auto elec suggested. They said she needed a trailer control unit and they could supply a second hand one for about 1/3 the price they quoted her for a new one, so that's being done tomorrow - fingers crossed!! :pray:

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brientim
Posts: 3
Joined: Tue 03 Feb, 2015 2:55 am
Model you own: w164

Re: W164 Trailer Wiring Issue

Post by brientim » Tue 03 Feb, 2015 3:02 am

The rear SAM may also need looking at

http://www.mbca.org/sites/default/files ... ing_sb.pdf

Wonky
Dernburg Wagon
Posts: 5
Joined: Fri 30 Jan, 2015 11:58 pm
Model you own: w164

Re: W164 Trailer Wiring Issue

Post by Wonky » Wed 11 Feb, 2015 8:19 pm

Thanks brientim. The place she took it to said it was just the Trailer Control Unit (part #B64541120) but they've been less than impressive so far............ :banghead:

Quoted her $330 for the part and $100 to fit. She's not silly so rang the local dealer who quoted her $230 for the part, then rang our auto elec who said 5 mins to fit and she could do it herself (he knows she's capable) or he could do it for her. It was what he suspected when she first took it to him but didn't have the equipment to be certain and didn't want her to buy an expensive part only to find it was a waste.

After she rang the place to tell them what she'd discovered and to organise picking the car up they rang her back to say if she could leave the car there (an inconvenience as she'd had to use my wife's car instead) they could get a second hand part in for $100 and fit it next morning. My wife and I went out of our way next afternoon about 4pm to pick it up and they hadn't even got the part in! We brought the car home so my wife could have hers back. That was over a week ago - have heard nothing more from them. :dontknow:

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olddog642
S Class
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Joined: Sat 27 Dec, 2014 1:15 am
Model you own: w201
Location: Canberra ACT

Re: W164 Trailer Wiring Issue

Post by olddog642 » Thu 12 Feb, 2015 1:58 am

Wonky wrote:Thanks brientim. The place she took it to said it was just the Trailer Control Unit (part #B64541120) but they've been less than impressive so far............ :banghead:

Quoted her $330 for the part and $100 to fit. She's not silly so rang the local dealer who quoted her $230 for the part, then rang our auto elec who said 5 mins to fit and she could do it herself (he knows she's capable) or he could do it for her. It was what he suspected when she first took it to him but didn't have the equipment to be certain and didn't want her to buy an expensive part only to find it was a waste.

After she rang the place to tell them what she'd discovered and to organise picking the car up they rang her back to say if she could leave the car there (an inconvenience as she'd had to use my wife's car instead) they could get a second hand part in for $100 and fit it next morning. My wife and I went out of our way next afternoon about 4pm to pick it up and they hadn't even got the part in! We brought the car home so my wife could have hers back. That was over a week ago - have heard nothing more from them. :dontknow:
Sounds like a bunch of jerks attempting to rip of a women, unbeknown to them she probably knows more than they do. Give them a wide berth
Stick with your own auto electrician they sound genuine.
cheers
Hylton
Daily driver
1988 190e 2.6 Almandinrot "Etta"

Wonky
Dernburg Wagon
Posts: 5
Joined: Fri 30 Jan, 2015 11:58 pm
Model you own: w164

Re: W164 Trailer Wiring Issue

Post by Wonky » Sun 15 Feb, 2015 10:10 pm

Yes, very disappointing Hylton. Someone from there had obviously done a business card drop at our auto elec which is why he sent her there. He's now binned the card as poison. :)

I didn't know who they were before she went there, only the location, so I Googled them and very quickly found them. Just goes to prove the old adage that you can't judge a book by its cover.

Very professional looking website, huge well equipped workshop offering servicing on all German prestige makes.

Steer clear!!

Mickey
C Class
Posts: 33
Joined: Mon 13 Apr, 2015 12:04 pm
Model you own: w164
Location: Sutherland Shire, NSW

Re: W164 Trailer Wiring Issue

Post by Mickey » Mon 13 Apr, 2015 12:28 pm

Hello, all. I am new here but I thought I could help with a similar experience.
I have a 2010 ML350 CDI. When I went to hire a caravan with LED lights, I hooked it up and the caravan lights didn't work. To cut a long story short, it is an issue with most modern European cars. My solution was to trot down to my local MB dealer and buy an adaptor which plugs straight into the car trailer plug and caravan plug. Cost me about $180. No other messing around needed and problem solved. BMWs, Range Rovers, etc all need the same thing unless it is built in to their systems these days.

Wonky
Dernburg Wagon
Posts: 5
Joined: Fri 30 Jan, 2015 11:58 pm
Model you own: w164

Re: W164 Trailer Wiring Issue

Post by Wonky » Sun 19 Apr, 2015 5:03 pm

Hi Mickey. Sounds like you were lucky and twigged straight away. My daughter's car unfortunately worked ok with the LEDs straight up so she assumed all was ok. It then blew something which cost her several hundred to fix in addition to then buying the adaptor. The guys at the local MB dealer (Berwick) were extremely helpful.

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