Evening all 👋

I've got electrical gremlins!

Are there any electrical BCM gurus here?! 🙏

Firstly, can anyone point me in the right direction to a layout of the BCM plug sockets, what they relate to??

A year ago I noticed my offside H7 dipped beam connector had melted at the earth point. I replaced it, still didn't bring the dipped beam back!

I drove on for a month, then the nearside dipped beam died on me!

I then brought a motorcycle and she's been neglected ever since, sorn and laying grubby 😞

I've got power to the fuses (50+54)

No visible breaks or melts in the loom.

A mechanic came out and plugged her in, poked his multi meter about for 2 hours, no power at the h7 connector. he left without a diagnosis 😭

Today I noticed the earth point under the fuel filter bracket was caked in oil, could this have been the culprit?

After researching a little deeper, I am wondering if I have allowed the BCM MOSFET to burn out, by continuing to use the lights until the nearside died?

Are these MOSFETS repairable by a specialist, or more costly than if I were to get a new BCM?

Appreciate your time guys!

Regards

Craig.

I don't think the BCM powers the headlights.

Will have a look at circuits later.

I have pinouts for BCM somewhere, but doubt they'll be relevant.

Cheers Pete.

Apparently there are no relays as such for the dipped beam, it uses BCM solid-state switching. The only relay I could find relating to headlights, is the bulb malfunction relay - 393.

No, that's the indicators, not headlights.

That the BCM controls, or the relay 393?

I've just ran a scan with the vcds and the BCM is showing a few faults, short to plus on them all.

BCM controls indicators via a solid state chip containing FETs. It doesn't control headlights at all, I believe.

Circuit scrutiny not far off now, or you can research yourself via handy link to mk1 workshop manuals that can be found on here.

Link to manuals (including wiring diagrams) https://www.briskoda.net/forums/files/file/76-mk1-fabia-workshop-manuals/

Thanks Pete.

I was going off what info chatGPT and google AI gave me.

So what does control the dipped beam, is there a relay I can't find? 🤯

I am determined to find the issue without paying anymore for professional help 😂 I enjoy it, but electrics give me anxiety!

Does your car have halogen or HID (Xenon) headlamps?

If halogen, there's just the rotary light switch, and fuses.

If xenon, there's also a starter unit after each fuse (near light clusters I think).

Cheers Pete, so good to speak to someone who knows their 💩!

Halogens I have.

So I have power to 50+54 fuses, do wires go straight from that point behind the fuse board, or is there something else before they split off down the loom to the headlight connectors either side?

With the one side going and melting, then the other side died, with no melting, confused me. I wondered what I saw online about the BCM eventually possibly cutting off the dipped beams completely if it notices a fault is still ongoing, is that a possibility?

Edited 17 November, 202517 Nov by Sirward
Didn't say all I wanted to

I think the only thing between fuses and bulb connectors is the connector pairs where the engine bay loom meets cabin loom at the firewall.

BCM still not involved!

Does your car have bulb failure warning system?

It does, that's what the 18 pin relay I mentioned relates to isn't it, 393?

I guess so. I'm not very familiar with it.

If you download the 2004 circuits from the link I gave above, and search the pdf for "bulb failure" you should find the relevant pages.

I vaguely remember taking one of those 'relays' apart many years ago, and finding that it was just a set of current shunts monitoring the feed current to each of the bulbs.

Did you check the bulb on nearside? And offside, come to that.

Edited 18 November, 202518 Nov by Breezy_Pete

Check the wattage of the bulbs fitted. My old van fried the connectors due to the previous owner fitting 100/80watt instead of 60/55watt. I did think the headlights were particularly good for a Fiat ducato. A bad earth can also cause things to heat up.

Alasdair

Cheers mate. I had tried three different sets of bulbs, standard h7 55w, still no joy.

Came accross this when looking. Not sure if its any help but it mentions running a wire from fuse 54 to actual headlight to check.

Thank you Alasdair! I'll check that thread out.

I managed to find this on scribd, which will help massively, unless it's the wrong one 😂

Thought I would update this for those who might be struggling with dipped beam issues.

As the diagram shows, the power for dipped beam is separate, it is fed from the headlight switch to the fuse board. Before the fuse board it splits into two, and feeds fuses 50+54. From there the yellow for nearside, and black and yellow for offside run straight to the headlight connector, then to the H7 bulb connectors.

My issue i believe (don't take my word for it) stemmed from an oil covered earth point behind the headlight beneath the fuel filter holder. This likely caused high resistance, melting the h7 first, then taking out the other dipped beam by finally heating up the switch terminal to the point it melted inside the switch.

Glad you found the problem. Its surprising the fuses didnt blow before the wire/switch melted but thats car electrics for you. Well done for tracing it back

Alasdair