# Marker lights



## GROUNDHOG (Mar 7, 2006)

The marker lights on the drivers side of our van are working incorrectly, sometimes they come on sometimes flash a bit and sometimes not at all.

I have taken the lights out and cleaned them, checked the wiring as far as possible and there seems to be nothing wrong. The dealer ( Marquis) have been first class and have also been through the system and cannot find anything. They have now offered to rewire the whole thing and replace the lights.

The Mercedes has the canbus wiring systems, before they do that anyone have a suggestion as to what it might be please.

As a clue when you turn the switch on they always come on instantly before going off again?

Thanks 
David


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## Rodav (Jul 21, 2012)

Hi David, It might be worth checking your AS handbook as I seem to recall seeing a relay for front marker lights in the circuit of our AS Nuevo, so it may not be anything to do with the canbus!
regards
Dave


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## sideways (Jun 2, 2008)

have you replaced a bulb any where in the sidelight circuit?


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## rayc (Jun 3, 2008)

I can't say for Mercedes vehicles but the high front and rear lamps and side markers on Fiat Ducato X250's are not part of the original vehicle wiring.
The sidelights / brake lights etc on Ducatos are switched via a control and bulb failure module. The additional high front and rear lamps and side markers are powered by bespoke fuses and relays seperate from this module. These are provided by the MH convertor. The relays are switched by a signal from the vehicle original wiring which detects the vehicle lights on. this signal wire is left somewhere for the MH convertor to connect to.
On my Chausson they were switched on via a discrete module located within the lower driver seatbelt housing. On my Rapido the extra fuse and relay are located under the dash by the cab fusebox.

You said "As a clue when you turn the switch on they always come on instantly before going off again?"

I therefore think that the lights and wiring are OK and the control signal is being lost. A simple check would be to find where the wiring leaves the interior of the vehicle to the outside. [On my Rapido there is a connector located within the lower section of the driver seat belt housing]. When I had problems I unplugged the plug / socket and fed 12v positive and negative directly to the outside. The lights came on and stayed on so I knew the problem was inside the vehicle. It turned out to be a dodgy fuse holder.

http://www.motorhomefacts.com/ftopicp-1074366.html#1074366

http://www.motorhomefacts.com/ftopict-117890-side.html+marker+lamps


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## sideways (Jun 2, 2008)

Hi ray i can tell by your posts your a competant electrician, i retired before canbus, can a wrongly fitted bulb make the light come on and then go off again please, its something i was told hence why i asked the OP


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## rayc (Jun 3, 2008)

sideways said:


> Hi ray i can tell by your posts your a competant electrician, i retired before canbus, can a wrongly fitted bulb make the light come on and then go off again please, its something i was told hence why i asked the OP


Well, wrongly fitted can cause differing problems depending on how it is making contact. A single light may come on/off but a series of them less likely. I recently helped my son in law find out why his rear light cluster was playing up on a Scenic. Trying to make logical sense was a waste of time as there were so many variables depending on side / brake and indicator lamp combinations. The fault was, as it often is, a dodgy earth.

Modern MH's are not wired as they used to be. Then you just connected the side markers into the side light circuits, in a similar way to tow bar electrics and possibly upped the fuse.
As I indicated in my post they are now likely to be a separate circuit with their own fuses and relay and only 'triggered' via a light on control signal from the vehicle lighting control module.
Different MH converters do it in different ways. The vehicle manufacturer merely leaves the signalling trigger wire somewhere to be picked up by the converter. Uncle Norms Adria and my Chausson and Rapido were all done in different ways.

Apologies to the OP if these digressions are not helping him.


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## GROUNDHOG (Mar 7, 2006)

Thanks that helps a lot, when it stops raining ( if) I will trace the relay and have a look at it.

To answer the question, No I have not changed any of the bulbs, the van is only a few months old and this problem has been there from day one.

Credit to Marquis they have agreed to fix the problem but sometimes you know how it is if I can fix it myself without a two hour round trip and another hour drinking their coffee then I will give it a go!

Thanks again all.....


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## poleman (Aug 31, 2008)

The canbus system will turn off that circuit if it detects a fault, as suggested incorrect bulb etc. If the lights always come back on and then go off this suggests a fault on that circuit. 

Sprinter chassis cabs are wired through an ECU to provide separate supplies to side lights (front) tail lights, rear marker lights (outer edge of original Mercedes lights), Number plate lights and side marker lights (orange ones down the side). If the body builder has say wired the number plate lights to one side of the marker light circuit the ECU will register an overload and switch them off. 

We have had Mercedes trucks register bulb failure lights because a bulb which isn't needed is not fitted, fit the useless bulb and the light goes out!


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## GROUNDHOG (Mar 7, 2006)

The plot thickens, when the lights are turned on without the ignition they work fine but as soon as you turn the engine on the drivers side marker lights ( except the first one) go out.

Marquis called in a specialist electrician who spent two hours trying to figure it out, checked everything and then decided it was a Mercedes wiring fault. Mercedes are now going to have a look but have said they have not heard of this problem before.

Fascinating to find out what it is in case anyone else gets or has the problem.


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## GROUNDHOG (Mar 7, 2006)

After hours of investigation by Marquis and Mercedes, both of whom have been really helpful, interestingly, it was a fault in the Mercedes Signal Acquisition Module. Mercedes SW had never seen it before. All I know it is not a cheap piece of kit so rather pleased it is all being done under warranty. :lol:


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## rayc (Jun 3, 2008)

GROUNDHOG said:


> After hours of investigation by Marquis and Mercedes, both of whom have been really helpful, interestingly, it was a fault in the Mercedes Signal Acquisition Module. Mercedes SW had never seen it before. All I know it is not a cheap piece of kit so rather pleased it is all being done under warranty. :lol:


It confirms that switching a lamp on or off is not the same in modern vehicle as it used to be.
A quick google of 'Mercedes Signal Acquisition Module' brings up loads of hits many by owners who found it almost impossible to get the fault diagnosed let alone fixed.

It may also be one of the reasons there are so many vehicles driving round with one or more failed lamps. Imagine getting the fault fixed whilst out and about.


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## oldun (Nov 10, 2005)

When I started fitting towbars to cars in the early 60's there were just two fuses. One fused for the 12V always live and one for the 12V switched by the ignition.

We called it the oldbus system, forerunner of the canbus system and it was marginally easier to understand.

Now everything on a modern vehicle is so complex that even the expert mechanics in garages are often confused by its complexity.


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## rayc (Jun 3, 2008)

oldun said:


> When I started fitting towbars to cars in the early 60's there were just two fuses. One fused for the 12V always live and one for the 12V switched by the ignition.
> 
> We called it the oldbus system, forerunner of the canbus system and it was marginally easier to understand.
> 
> Now everything on a modern vehicle is so complex that even the expert mechanics in garages are often confused by its complexity.


I have just replaced an intermittent windscreen washer pump on my X250 Ducato.
Whilst waiting to get the new pump I looked at the circuit of how it worked. The steering wheel arm switches connect to the body computer. Operating the washer switch causes the body computer to operate the wipers 4 times and then a delay for a final wipe. There is also an output from the computer which operates a relay which feed power to the pump via a fuse and the relay, which are in the engine compartment fuse box. 
I was able to change the pump in about half an hour as it was a bit fiddly. Fiat procedure is to remove the headlight but I managed to do it without doing that.


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