Flickering Fog Lamps

[StuartO]

Driving home in rain, on dipped headlights, I noticed that our front fog lamps were flickering on and off.  It got owrse and must have been very distracting to oncoming traffic.  I switched the fog lights on, so that at least they were steadily on.

 

Mine is a2006 Fiat/X244 based Hymer A Class.  Anyone think of an explanation?

 

[StuartO]

I've bumped this thread because I'm a bit further forward, although I do still need expert comment or advice.

 

The fuse for the foglamps is F09 in the box under the bonnet and this was intact.  There is an associated relay in the same fusebox which I have removed - and I have ordered one to replace it.

 

As far as I could tell both fog lamps were flickering on, so my current theory it that the fog lamp relay has sticky contacts.  What I don't know is how the turning lamp circuit works, which switches on only one fog lamp when you turn at slow speed.  I can't remember whether this requires the relevant indicator to have been activated as well as the headlamps to be on but this would be one way of controlling the turning lamp circuit and it's something else I can functionally test.  The relay used for the fog lamps seems to be identical to the one next door which does the horn, so I could swap them over as a test as well.

 

Any thoughts you chaps?

 

 

 

[Brian Kirby]

StuartO - 2017-03-03 8:56 AMDriving home in rain, on dipped headlights, I noticed that our front fog lamps were flickering on and off.  It got owrse and must have been very distracting to oncoming traffic.  I switched the fog lights on, so that at least they were steadily on.

 

Mine is a2006 Fiat/X244 based Hymer A Class.  Anyone think of an explanation?

Not a solution, Stuart, just musing! From your post above and your subsequent post I understand that the front fog lamps were both simultaneously flickering on intermittently, when they were, in fact, switched off? Therefore, as you were later able to turn the fogs on and they stayed on without flickering, I think you can discount fuses. What I guess can't be determined is whether the headlamps were also flickering? Also, as it was raining, whether the fog lamp flickering related in any way to windscreen wiper activity.What you seem to have experienced is an intermittent power supply to the fog lamps via an "illicit" source. Possibly that relay, but it would first need power on the actuation circuit and, with the switch off, there should not have been power. Have you checked the connections at the fog lamp switch and adjoining switches, in case a loose live connection is playing havoc?Otherwise, what was actually getting wet under the bonnet? My first guess (not in priority order!) would be that water was the culprit in some way. My second guess would be that there is a poor earth connection from something like the windscreen wipers, that was feeding into the fog lamps circuit.The flickering suggests to me either water making a connection it shouldn't, or a poor earth on another consumer causing the current to follow an earth path through the fog lamps.My final thought would be to check that famous engine earth strap.The problem with A-Class vans is that all the lights are mounted on an electrical insulant, and so must have their own, dedicated, earth wiring. In rain, with the headlamps, wipers etc. all working, quite a bit of power is flowing and so, if one of the earth paths has an undesirably high resistance, the current will use any available path that offers a lower resistance. If that is the fog lights circuit, so be it! I think I'd probably start with the engine earth strap and, if in any doubt, replace it with a well sealed, insulated, battery negative connecting cable of appropriate length. Halfords is one source of such cables, ready made in a variety of lengths.

[StuartO]

Very helpful, thank you Brian.

 

It wasn't raining continuously, although it was heavy at times and as i recall the problem just gradually got worse, not necessarily because of rain or water ingress. I didn't notice any correlation with use of the wipers.  I'm sure both fog lights were flickering, not just one.  Switching on the fog lights definitely cured the problem in that they came on immediately and remained on steadily.  I didn't notice any fault with the headlights.  The fuse box under the bonnet is extremely well protected against weather and the fuse/relay board inside is pristine.

 

I've already ordered a replacement relay (handy to have a spare anyway) and that will be here in a day or two so I'll wait until that arrives before looking into the earth strap idea.