Technical Fog light problems

[ChrisCM]

I have a 2015 Ducato based campervan. I have problems with the rear fog lights. 1. The fog light indicator in the dash has stopped operating but the fog lights come on when the switch is pressed. 2. I have permanently chassis mounted bike carrier with complete light clusters including fog and reversing lamps. When the bike carrier is plugged in, via a 13 pin towing type socket, the fog light on the carrier comes on (and all other lamps work correctly) but not the main vehicle fog lights and when I unplug the carrier then the vehicle fog lights come on. All the other carrier / vehicle combinations work as they should.
Anybody any idea what is going on here.?

Thanks!

 

[rayc]

It appears you have a modification which disconnects power to the vehicle fog lights when a trailer is connected. This is the norm in the caravan world to prevent the fog light illuminating the front of the caravan and effecting the drivers view to the rear. I have not towed for many years, since the 7 pin socket was standard where the fog lamp interrupt was part of the socket. I do not know how it is actually done on the 13 pin one but it could be a separate relay??? https://www.rydertowing.co.uk/towbar-relays/fog-cutout

 

[ChrisCM]

Thanks Ray,
Of course! Hadn’t thought about that! I’ve got round this problem by removing the bulb from the bike holder ( the vehicle ones arnt obscured by the bikes) my main worry is the indicator light, I need that to pass the MOT. I had thought of wiring in a small led to the switch to act as an indicator but I fear that it’s not just a simple switch, hopefully someone on the forum may have an idea?

 

[jackwhoo]

Did the fog light tell tail work before the bike rack fitted?
After bike rack fitted?
Who fitted bike rack?when?
Are you using a 7pin to 13 pin adapter between van and bike rack?

 

[ChrisCM]

The rack has been on the van since I bought it several years ago and the indicator light has always worked. I have just changed the carrier light clusters and was testing the lights and found the “problem” with the rear lights and rack light, but thinking about it it’s probably always done this (as it should!) and I just haven’t noticed as I’ve not had much occasion to use them. The rack was fitted and wired by a Dutch Company, Busbiker, the manufacturers of the rack. The interface uses a 13 pin plug and socket with no 7 pin adapter. The rack has a facility to attach a trailer hook so can be used to tow a trailer, which I have done, and the lights, which plug into the 13pin socket, work as they should on the trailer.

 

[jackwhoo]

Thanks for the extra info.
I like your idea of a separate led tell tail for fog lights.
I have a feeling the easiest way is run an extra wire from the bike carrier fog light under the vehicle to the cab for the led tell tail.

 

[HughJampton]

It isn't a blue Campscout, is it?

I'd carefully check the wiring if I were you. The lighting boom and loom Buscamper/Busbiker used was designed for LHD, and they had to modify it and the lighting itself for RHD (since the reversing light and fog-lamp were wrong-handed as standard). I pointed this out to them before fitting, and they added a small fee for correction.

I'm not sure how that could affect the operation as described (I suspect they use a non-Fiat canbus interface to operate the lights) but, that, combined with cluster replacement certainly raises a few questions.

 

[ChrisCM]

Jack, yes I may have to do that, I’m having an auto electrician look at with a view to taking a feed from the switch but as it’s a momentary push switch there must be a circuit board somewhere which latches the out put to the fogs, either with a latching relay or electronically so may not be as easy as olden days when switches were switches
Hugh yes, aware of that, the carrier is wired to conform with the socket which has fog and reverse reversed. I don’t think changing the clusters caused the problem, as it was a like for like replacement with incandescent bulbs .I’ve swapped the connections on my trailer plug so that works ok. My van is a gold Devon Aztec XL.

 

[DACS]

I suspect that the warning light on the dash is also used to indicate a failed bulb. By replacing the tungsten lights with LEDs you have probably reduced the current drawn so that the system assumes that a bulb has failed. This is a common problem when towing caravans with LED lights. You could probably overcome your problem by adding a resistor across the rear fog light circuit to pass enough current to fool the system but you would lose the facility to check that the lights are actually working.

 

[rayc]

Jack, yes I may have to do that, I’m having an auto electrician look at with a view to taking a feed from the switch but as it’s a momentary push switch there must be a circuit board somewhere which latches the out put to the fogs, either with a latching relay or electronically so may not be as easy as olden days when switches were switches
Hugh yes, aware of that, the carrier is wired to conform with the socket which has fog and reverse reversed. I don’t think changing the clusters caused the problem, as it was a like for like replacement with incandescent bulbs .I’ve swapped the connections on my trailer plug so that works ok. My van is a gold Devon Aztec XL.

The fog lamp circuit is part of the Body Control Module [BCM]

 

[ChrisCM]

I suspect that the warning light on the dash is also used to indicate a failed bulb. By replacing the tungsten lights with LEDs you have probably reduced the current drawn so that the system assumes that a bulb has failed. This is a common problem when towing caravans with LED lights. You could probably overcome your problem by adding a resistor across the rear fog light circuit to pass enough current to fool the system but you would lose the facility to check that the lights are actually working.

Sorry, you misunderstand, I did not replace any bulbs with LEDs, the clusters I replaced were like for like with the old units which had got damaged and corroded, both old and new are fitted with incandescent bulbs and the new ones are all working, with the exception of the fog bulb in the carrier o/s cluster which I removed to resolve the fog light issue.

 

[ChrisCM]

The fog lamp circuit is part of the Body Control Module [BCM]

Sounds expensive! I think I’ll probably go down the route of a wire from the fog lights to the dash if I can’t pick up a feed in the dash.

 

[rayc]

Sorry, you misunderstand, I did not replace any bulbs with LEDs, the clusters I replaced were like for like with the old units which had got damaged and corroded, both old and new are fitted with incandescent bulbs and the new ones are all working, with the exception of the fog bulb in the carrier o/s cluster which I removed to resolve the fog light issue.

Perhaps when the carrier is plugged in the 'towing relay' circuit is expecting to see that the lamp is operational by its current draw. Maybe this is then used to operate the fog lamp on indicator?
Be that as it may what happens when the rack is not plugged in? I assume the van fog light illuminates but still no indication on the dash?

 

[HughJampton]

I think the OP has confirmed that the dash light is inoperative under all circumstances.

Having thought about it, I believe Buscamper used a bypass relay, with an additional feed from the vehicle battery (my memory isn't what it was, though!).

Patently, when the additional lighting unit is attached, all lights on that should reflect (pun intended) those on the vehicle, except the fog lamp, which should be (and is) inhibited.

Research indicates that this inhibition is often accomplished by a cut-out in the 13 pin socket, which should inhibit the vehicle light if a plug is in place. I'm simply trying to understand the workings, and not sure that this helps at all, as I can't think of any way a "stuck" socket cut-out (it does happen) could cause the dash light problem when all else is working.

 

[ChrisCM]

Perhaps when the carrier is plugged in the 'towing relay' circuit is expecting to see that the lamp is operational by its current draw. Maybe this is then used to operate the fog lamp on indicator?
Be that as it may what happens when the rack is not plugged in? I assume the van fog light illuminates but still no indication on the dash?

Yes, correct, still doesn’t work when the rack is unplugged.

 

[ChrisCM]

I think the OP has confirmed that the dash light is inoperative under all circumstances.

Having thought about it, I believe Buscamper used a bypass relay, with an additional feed from the vehicle battery (my memory isn't what it was, though!).

Patently, when the additional lighting unit is attached, all lights on that should reflect (pun intended) those on the vehicle, except the fog lamp, which should be (and is) inhibited.

Research indicates that this inhibition is often accomplished by a cut-out in the 13 pin socket, which should inhibit the vehicle light if a plug is in place. I'm simply trying to understand the workings, and not sure that this helps at all, as I can't think of any way a "stuck" socket cut-out (it does happen) could cause the dash light problem when all else is working.

Yes, I believe there is a relay attached to the battery as there is a fused lead labelled “Busbiker” which disappears to the rear of the van. I tried removing this fuse and the effect on the carrier lights was to stop the indicators working on the carrier, all other lamps on the van and carrier still work. I’m coming to the conclusion that the failed indicator light has nothing to do with the carrier and that linking the two was as a result of me forgetting that the van fog lights would be inhibited when the carrier or trailer was plugged in and I just happened to notice the lack of an indicator light as I was getting the van ready for its MOT.

 

[jackwhoo]

cheapest, quickest, neatest option is to run an extra wire under the vehicle from the trailer socket to a new tell tail light on the dash. Plus advantage of not cutting into original vehicle wiring.