tow bar loom

dodgy

Member
Hi all, does anyone know what's involved in getting the wiring loom (working) connected for the tow bar on a 2010 ex ambo, I have a factory MB tow bar loom with 7 pin flat plug to plug into the van loom but the van loom is not working.
The van loom only has one wire with power to it, no tail lights, no brake lights, no blinkers.
I looked under the drivers seat for the start of the loom (yeah what a mess under there) but didn't locate it.
any help would be greatly appreciated
thanks
dodgy:thumbup:
 

Lams

Crafter driver
Hi dodgy, I just completed my own install not long ago. Best bet is to trace the wiring from the towbar to see where that leads you. Mine has its own electronics controller box and 2 fuses powering it, so the first step would be to make sure it's all powered and earthed properly - good luck!
 

dodgy

Member
yeah just had a better look at it and the loom starts from under the drivers seat with four loom connectors, what they plug into is the million dollar question. looks like it's missing some bits.



 
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dodgy

Member
does anyone on here have the factory loom connected, and know what the four ends of mine are supposed to be connected too.

thanks dodgy
 

Eric Experience

Well-known member
Dodgy.
Those plugs are factory wiring not trailer stuff that I have seen. The trailer plug needs one heavy red wire to power the relay box and then 5 small wires from the light ccts. Most installations get the small wires from the loom where it crosses the rear above the spare wheel. As I have said many times it is better in the long run to remove all the ambo Wiring. Eric
 

dodgy

Member
Thanks Eric, I just assumed the loom was the tow bar loom, it starts under the drivers seat at them four plugs, and they are factory cause the loom tape is the material type like the rest of the factory loom, it runs under the van on the passenger side and stops at the very rear beside the spare tyre, it has two connectors male and female that plug together.
I got hold of a factory bar with the factory loom and seven pin socket that also had the two male/ female plugs, same as the van loom plugs, I fitted the bar and connected the plugs together,, male van loom plug to female tow bar loom plug and female van loom plug to male tow bar plug.
heres a pic of said bar, sorry no close up of plug atm.


pic of bar fitted


ok so now I think I'm all done...nope doesn't work, so I get my multimeter out and chase the loom with one end of the multimeter stuck up the seven pin socket and the other end in them four plugs under the seat and they were all related back to the seven pin tow bar socket.
 
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KimolosMike

New member
Dodgy, when I fitted the tow bar to my 2006 using the MB loom, I had to take the van to the stealership so that it could all be activated.
 

Oldfartt

Active member
OK Guys,
Here is my information ... for what it is worth.
The connectors under the drivers seat is part of the pre-install for the trailer fit out. It is not AMBO wiring but is MB pre-install. They plug into a "Trailer control module" which you need to purchase for somewhere over $400. Not normally fitted as standard unless the tow bar is ordered at time of build. Then you need a cable to take you from the two connectors near the spare tire to connect to the seven pin plug to be fixed near the tow hitch. More money. Then you need to connect the Trailer control module to the Data bus with yet another cable which runs to behind the side panel below the drivers door hinges (RHD). There is a data bus bar hidden behind the wall panel.
Then you need to take the van to the dealer who will need to activate the system using the OBD diagnostic port. Hope it all works!
The one useful feature of the pre-wire is the continuous 12V feed (thick red wire) to the rear connector near the spare tire. The 12V feed originates from a fuse panel near the bonnet release and behind the OBD port.

Now, the most cost effective (and I believe reliable) way to wire the trailer connector is to get a trailer control from and alternative supplier which taps into the existing rear lights as Eric notes. The modules take a low current voltage from each light, tail,brake,stop, turn, and uses the previously mentioned 12V circuit to relay switch the trailer lights. This means that the sprinter management system is isolated from the trailer and is not upset by the addition of extra heavy currents, which otherwise would bring up alarms and maybe LHM.
Here is what I have in my Motorhome.

Cheers

Ross
 

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Eric Experience

Well-known member
Dodgy.
Just shows we never stop learning. If that is factory prewire I would only use the heavy red to power a relay box and then tap into the loom for the light ccts to the relay box. Thanks Ross. Eric.
 

dodgy

Member
Thanks all, I would have liked to have just connected the thing together and go but that didn't happen, I will look into the Trailer control module and the harness to the data bus that Ross talked about, if all seems to pricey and not worth the effort I will just use the wiring kit that come with the Australia tow bar kit that I have here, should have just used it to begin with but didn't know the Mercedes benz system was gunna dick me around.
thanks guys
dodgy.
 

Huski

Member
Hi Dodgy,
Just did the trailer wiring on my 2006 ambo. We just used the wiring that came with the kit and tapped into the left light wiring for everything except the right indicator. We found a relay that had constant power sitting in the rear tail light area and used that. Everything seems to be working fine - not sure if the relay is anything to do with ambo wiring or the original mb wiring - but it works. During the process we thought something was wrong when 2 small high power leds - the red and blue emergency lights on the rear step - kept turning on each time we turned the lights on and couldn't work out what we had done. Turned out that if you have the rear doors open and turn on the headlights, this causes the emergency lights (at the back only) to be activated. With the lights on, and the doors closed, they turn off. Learning about the ambo fitout every day.
 

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