Front fogs not working

[robjmccarthy]

Hi,

I have a 2014 custom, with the front fog lights separate to the main light unit (the fogs aren't in the main unit, these aren't the corner lights).

20230527_100040.jpg

I've replaced bulbs, but they still don't work.

I've also checked fuse #8 I'm the BCM fuse box (meant to be the fog lamp supply).

Any ideas, or where to check next, would be greatly appreciated.

Many thanks
Rob

[noeljary]

Hi,

I've attached the full wiring diagrams for the front foglights for your custom. Sounds to me like you'll need to start poking around with a multimeter.

Screenshot 2023-05-29 at 01.40.34.png

This is the wiring from the BCM to the lights and grounds. It's unlikely both grounds are bad, and the diagram indicates other devices use those grounds. I'd be checking with a multimeter whether you're getting any voltage at the bulb connector, (the bulbs not lighting suggests you're not), but maybe also check with a different ground.

Tracing back from there, I'd be looking at the output from the BCM with the multimeter to see if you get voltage at this point, if you do, then you've probably got a broken wire to the bulbs. If not, then also check that there's voltage getting to fuse F8 with the multimeter, which should have 12V at all times.

If nothing by this point, it probably leaves the relay inside the BCM, and the signal reaching the relay to activate the coil. This will be much harder to check, as it's buried in the BCM and theoretically not serviceable. That said, the diagram suggests it's an actual relay - do you hear any stereotypical relay clicking noises when you press the button?

Screenshot 2023-05-29 at 01.40.25.png

In the first generation models like yours, the light control buttons were connected by a LIN bus to the BCM instead of individual wires for the buttons (on later models). That's harder to diagnose without an oscilloscope, but if the other lights are working, then you can assume the connection between the switches and BCM is good, but it won't rule out the button itself. At that point you'd likely need to swap out another switch module to confirm.

Hope this gives you a start on fixing it!

Noel

[robjmccarthy]

Thank you Noel for your explanation.

In ttheory it all makes sense, but unfortunately I may not be the best to try and find it.

Can I ask, where on the BCM would you check re this that you said "Tracing back from there, I'd be looking at the output from the BCM with the multimeter to see if you get voltage at this point,".

No power to the bulbs, so I want to check if it is at least leaving the BCM as you suggest.

I can see where the loom goes into the body of the van (it literally is behind the BCM from the engine bay.

[noeljary]

So to check the output at the BCM, you'll need to check the output of pin 16 on connector C2280B on the BCM - the diagram below doesn't label the pins specifically, so hopefully there will be numbers on the connector, also, hopefully only the one yellow-orange wire so you can identify it easier!

Screenshot 2023-06-01 at 21.43.05.png

I found a picture on from google images of the connectors in question - as the wires exit at a right angle and there is no easy access to the back of the crimp lugs, it looks like you'll need to open the connector up somewhat to get access to be able to put the multimeter on the pin, you may need to get a little creative here. I've done this in the past on similar connectors using paperclips to get into the hole where the crimp lug is buried, and measure from here to a cab ground point. As you'll need the connector inserted into the BCM while testing, you'll want to be careful not to short it to any of the other pins.

For checking the 12V to the fuse, there should be small bits of exposed metal on each side of fuse F8. Assuming the fuse is good then you should be able to measure 12V from either of these to a cab ground point.