Technical Fiat ducato Dethleffs MH side/tail lights not working

[Kloppy]

Hi everyone, just joined, I have and issue with drivers sidelights not working Fiat ducato 2012 on a Dethleffs Motorhome. Passenger side lights are fine. All bulbs are fine,earths are good as brakelamps and headlamps working fine.
I believe that sidelights/tail lights are not fused but are fed from the Canbus system with an overload facility?
any ideas how to reset this or where the “feed” originates from, relay/connector block etc? Im struggling to find any meaningful wiring diagrams. I am electrical although not auto. Any help appreciated as I cant get the MOT without the lights working .Been under the van for a week tracing cables!
Thanks

 

[rayc]

You are nearly correct. The sidelights[front and rear ] are switched by the Body Control Module {BCM}. The BCM has resetable fuses that will only reset when the fault is cleared. I have tried to attach the sidelight package from a DVD manual but when saving to pdf the schematics loose their sharpness. If you need better let me know and I will TRY to take screen shots in jpg format. Be aware that in the drawings F010 and F011 are shown as headlamps. In this context it means the housings and the drawings show the connections for the sidelights within those housings.
Page 6 shows the positive signals from the BCM which switch the sidelights on at Pin 4 of the headlight unit multi connector.
I have not tried it but you could the swop the headlight modules over [I know they will not fit into the housings] and see if the fault remains on the drivers side or not.

 

[rayc]

Can you confirm that the rear and front sidelights do not work on the drivers side [ for some reason when I first read your post I thought it only applied to the front].
The front and rear lights on each side are independently fed from the BCM. [see page 6]
Have you checked the number plate bulbs?

 

[Kloppy]

Hi rayc,
Thanks for the prompt supply, first look on my phone the info sent looks readable, the front sidelight (positioned within the dipped beam headlight, separate supply and lamp), the high level rear marker lamp and the rear tail lamp are out all on the drivers side, the rear tail lamp being a dual element lamp with tail and brake lamp , the brake lamp is fine and thus the earth. There is no 12v to any of these lamps, there is a relay under the passenger seat which fires when actuated by the steering column stalk sidelight/dipped beam switch. But I cannot see what this relay is or where the cables feed from any manuals etc.
There is a tow bar relay connected into the circuit via a can plug/wiring at the driver footwell,the tow bar works perfectly although the tail lights are commoned up on the out going side of the relay. I suspected this intitially but it is wired as manufacturers instructions and if disconnected has no effect on the issue, the passenger side equivalent of the faulty lights all work perfectly with this tow relay connected. If the 3 lights were connected within a loop I would suspect a bad wire/connection, if they are fed separately it may point to a module fail?
Thanks

 

[rayc]

Hi rayc,
Thanks for the prompt supply, first look on my phone the info sent looks readable, the front sidelight (positioned within the dipped beam headlight, separate supply and lamp), the high level rear marker lamp and the rear tail lamp are out all on the drivers side, the rear tail lamp being a dual element lamp with tail and brake lamp , the brake lamp is fine and thus the earth. There is no 12v to any of these lamps, there is a relay under the passenger seat which fires when actuated by the steering column stalk sidelight/dipped beam switch. But I cannot see what this relay is or where the cables feed from any manuals etc.
There is a tow bar relay connected into the circuit via a can plug/wiring at the driver footwell,the tow bar works perfectly although the tail lights are commoned up on the out going side of the relay. I suspected this intitially but it is wired as manufacturers instructions and if disconnected has no effect on the issue, the passenger side equivalent of the faulty lights all work perfectly with this tow relay connected. If the 3 lights were connected within a loop I would suspect a bad wire/connection, if they are fed separately it may point to a module fail?
Thanks

Don't be too hasty in suspecting the BCM as in the previous post with the same problem it turned out to be the sidelight bulb on that side.

 

[Kloppy]

Hi,
I have checked all the 3 side lamps lamps with 12v they are fine, all wattages are as manufacturers recommendations (I had read somewhere this can trip the BCM) both rear plate lamps are operating. All marker lamps at low level are illuminated

 

[rayc]

Hi,
I have checked all the 3 side lamps lamps with 12v they are fine, all wattages are as manufacturers recommendations (I had read somewhere this can trip the BCM) both rear plate lamps are operating. All marker lamps at low level are illuminated

The amber side marker lamps are normally on separate non Fiat circuits provided by the MH convertor so can ignored for your investigation. The drawing on page 6 of the pdf show the number plate lights to be on a separate circuit from the BCM. The fact they are working shows that the input signal to the BCM is ok so it would appear to be the separate output feeds from the BCM to the front and rear sidelights on the faulty side that are suspect.
What to do next is the question? I would remove the connector from the headlight module on the faulty side and also remove the side/brake light bulb from the rear. Remove the bulb from the high level marker on that side.
Then start replacing one at a time and see what happens. I think any more tracing of wires etc is a waste of time at this stage.
If all else fails I guess it will have to be connected to a tester such as the Fiat Examiner which should enable each circuit to be switched independently etc

 

[Kloppy]

I will get on it in the morning, unbelievably to get at the front lamps the whole lamp body and associated front trim has to be taken to pieces, the coolant, brake fluid tanks etc make sure you cannot get to it, don’t think the designers ever work on their vehicles, hopefully before I do that I will try and fine an outgoing from the bcm

 

[rayc]

I will get on it in the morning, unbelievably to get at the front lamps the whole lamp body and associated front trim has to be taken to pieces, the coolant, brake fluid tanks etc make sure you cannot get to it, don’t think the designers ever work on their vehicles, hopefully before I do that I will try and fine an outgoing from the bcm

It is a coach built and not an A class? It is sometime since I had the X250 version but can't you just remove the multi connector to the headlight module? In any event a couple of screws in the trim above the lamp and one in the trim below and it can be removed completely.

 

[Kloppy]

Hi
traced the fault to a short on the high level marker that originated from a tee connection on the Dethleffs side of the Fiat to Dethleffs connector plug/socket. This is just behind the passenger side rear wheel near the springs.
The short was either a cable rub or tight radius prob caused at manufacture and had eventually broken down. Couldn’t access the cable as it was routed over the chassis so had to rewire from the connector.
All working MOT booked.
Thanks for all the replies really appreciated I now have more knowledge and info for any future issues.