Hi...Brand new to this site, but looking for advice or help in resolution to an electrical issue..

I had my 1.6tdi Mk2 Fabia (11) estate put in for a pre- mot test. The only thing that came out of it was a non working rear fog lamp. They changed the bulb but still no joy.

When I picked it up, I took it to Halfords and had it test on the meter. It showed 2.47 coming through the wiring...The dashboard light comes on showing it as working but nothing at the back end, just minimal volts but not enough to power it up.

I am definitely not anywhere close to being a auto electrician and trying to book a knowledgeable one is proving difficult in my area.

Would I be close in thinking that the fault lies between the rear light cluster and the dashboard electrics?

Any constructive advice would be really appreciated.

Thanks

are the minimal volts coming from the actual bulb holder? Have the wires prior to the holder been tested too? I ask as holders can get corroded and prevent power getting through. If there is not enough power at the actual wiring harness next to the rear bulb holder, it may be a damaged wire somewhere along its route. Fabia's (And other VW vehicles) Have been prone to having wires snapping in door bellows, etc so perhaps a wire is fractured somewhere here, too. I don't think the wires go through the boot/hatch for lights but they may pass under the rear seat or under internal door sills, etc. 

 

Just a thought, would that voltage be enough to fire up an LED bulb?  Perhaps not as its more wattage then voltage so that may be a non entity but if it worked, the job is done!

Hi Bud and thanks for your reply.

Yes the volts are coming from the bulb holder itself. While the guy from Halfords had the light and bulb holder out I took a look at it. To be honest, it looked clean. I couldn't see any sign of erosion or muck.

Here's the things..I had recently used the factory fitted ' removeable/concealed ' tow bar. As it was a 13 pin I needed to buy an adapter to convert to 7 pin. This may be a complete coincidence that it doesn't work now, but I can't help but wonder?  I did speak to a friend about it and he said he doubts very much that that had anything to do with it. By the way the tow board lights worked perfectly.

My one fear of all fears is auto electrics. It's not like needing a new exhaust or tyre etc...you can see what needs to be done. With electrics, a skilled man could walk up to it and fix it within seconds, or notice it, fix it, then play it out..it's the uncertainty of it all. 

As far as the LED bulb test?... to be honest I haven't tried that...and to be even more Frank, I wouldn't know how to do that. But that's a great point you make. Just out of interest, can you buy LED bulbs that are as large as standard vehicle bulbs?

If the adaptor is still connected then that may make a difference as it "Plans" To show the lights on the trailer being towed, not the car so this is very worth investigating. Make sure you have removed it completely and did not short/ remove any wiring to for it.

 

On the LED bulb point, many owners fit them and some mention getting a false bulb out warning which means you may need a small regulate/rectifier fitted. These are usually added inline so you plug that in the wiring and then fit as normal. A kind of extension, if you will.

Hi Bud,

Yeah the adaptor was removed after the test at the pre MOT check and once removed it was tested again THIS morning by the really helpful guy at the local car parts shop. He checked the socket, fitting and used a needle type tester which had a small bulb in it. Apparently,  it now has no current running through it. This guy did mention that the meter used at Halfords may have shown some sort of residual power at the time. The guy this morning also checked the wiring directly behind the light socket by pressing the needle tester through the sheath but with no sign of power. He also checked the fuse and that was good too.

Not only am I perplexed but the guy this morning who checked what he could, also seemed perplexed too. We kinda both agreed that fixed wiring doesn't go cruising the streets at night and come back to the car bruised and the worse for wear.

UPDATE:  I rang a auto electrician who by sheer chance has rang me while typing out this message. I explained that the sockets, fuse and panel was good. He suggested it might be the Body Control Module?.. but he said, "There are ways round that" like fitting a independent switch which doesn't fill me with joy to be honest.

Now all I have to do is ring him at 11am tomorrow (Friday) to see if he can fit and in somewhere soon.

What chance finding a BCM at the breakers?

Your advice has been sound...thanks Buddy. If you think of any other options , they would be very gratefully received. Thanks Mrgf.

I am not sure which module you might need and breakers yards often want as much as dealers for new anyway so its worth getting the fault found, first. You may then have a little sorting time but I am assuming you need it for the MOT. 

I think your guy was suggesting perhaps some wiring from a live source, to a simple switch, running to the rear though the car somewhere and connecting up to the bulb, to give it a "New" live feed. It may be a quick bodge to get the MOT sorted as I don't think there is any regulation for there foglight to operate from the normal light switch at all. You might find a cheap switch at Halfords, perhaps one with a light inside to remind you it is on and stick it where some models have heated seat switches. You could either remove the little plastic panel and kind of wedge a switch in there or try actually fitting one into the plastic cover. If you ever fix the proper system, you could then slip in a new little cover. You could find other places to fit it but you'll want to see it in order to use it and show the MOT guy that it works. 

 

Also, have you actually checked the proper switch is actually functioning anyway?  You need the key switched on, lights turned on and pull the switch either once if no front fogs or twice if front ones are fitted (Just in case you are not operating it correctly as sometimes people only pull it once). The switches themselves can fail, though. I had mine replaced under warranty as it failed to turn the headlights on!

 

P.S> it might be worth putting up your location as sometimes, others may be nearby to offer assistance.

Edited 1 March, 20197 yr by mrgf

If it was me, I would disconnect the towbar electrics completely, then test the foglight.

 

The tow electrics as mentioned turns off the rear fog on the car. It sounds to me that the car "thinks" there is a trailer connected so its disabling the fog light.

 

I doubt the body module is faulty, to much of a coincedence here.

 

The fog cutout switch is as far as I can see is a seperate part and has a 3 pin connector. Have a look underneath at the towbar wiring, if you see a 3 pin connector connected "before" the loom goes into the car, disconnect it and try the fog light, it "may" be just inside the car (boot) near where the wiring loom comes in through the large grommet, again if you see it, disconnect it and try the fog light.

 

Failing finding that connector, under the driver seat is the trailer detector unit, disconnect that and try again with the fog.

 

When you say fuses were checked, just confirm fuse 37 (7.5amp - Brown) was checked, in the fuse box below right knee (clip off cover panel)

Edited 2 March, 20197 yr by UrbanPanzer