I think I'm getting to the bottom of the problems with my high beams not working... I have fairly confidently narrowed it down to the BCM.

Briefly, the BCM gets a signal from the stalk/switch and is supposed to activate pin 9 which tells the headlamp relay to turn on the lights. I have a signal from the stalk (blue light comes on).. and activating the relay manually works the lights... so it looks like the BCM is not passing on the signal to the relay.

N.b. I have tried a different stalk and even an alternate (battery side) fuse box during my investigations. I'm 90% certain that the BCM is the main culprit.

Now... I have removed the BCM and taken the lid off. On the PCB it looks like there are two tracks/circuits to the area around Pin 9.. (I can't quite see under there) and if you follow the tracks out, one of them has a small tarnished "break" (blackened/melted?) in it.

I have circled Pin 9 and "break". Does it look dodgy to anyone who knoes.... or is it normal? My mate Ollie who used to repair missiles for the navy says it looks like a repair..?

How can I test the circuit from the pin to the track just ahead of the "break", to see whether it is part of the Pin 9 circuit or just coincidentally close to it? If I can get a signal through pin 9 from just before the "break"... I'll be able to test what happens to the circuit on the other side of it.

Ralf S.

Here it is.. you can zoom in..

Using a stanley blade or similar, scrape the green gently off the track to expose a couple of millimeters of shiny track (might be copper, maybe aluminium). Do this either side of the break but close to it.

Using a multimeter set to continuity (will give Audio tone, or a low reading of a few ohms to show continuity):

First test for continuity between the two scrapings to see if the break is actually a break.
If no tone (break confirmed), next try between pin 9 and the pin-9-side of the PCB track (presuming the connector is the upper red circle?). You should get tone.

Now confirm with a test between Pin-9 and the other scraping (should not get tone).

Presuming you get tone on one side of the break and not on the other, the fix would be to solder a small piece of single core wire (or the leg off an electrical component for example) to the two scaprings, bridging the break. First add a tiny bit of solder to both scrapings. If it's taken to the track properly, you should get a little hump, rather than a blob or a sphere.
Holding it in tweezers, tin both ends of the wire, then press the wire onto the two humps and melt the hump again. The wire should "embrace" the solder and it should look nice and shiny. If the wire sits in the solder like Homer in a bouncy castle then it's not taken and you need more heat, or a bit more flux (tiny bit more solder if you don't have flux).

Sorry if this is teaching you to suck eggs, might be useful info for someone else though

If the PCB track has burnt up its highly likely a short on the output has caused the copper track to act as a fuse,do you have a better photo as I can't enlarge on my tablet.

Ralf S. said:

Here it is.. you can zoom in..

Click to expand...

It's tiny but it's very much there! I'd say you may well be on to something.