Wyevalley wrote:

A bit more info chaps.

It isn't going to be as easy as I first thought.

I managed to find a 2014 wiring diagram with HID headlights and the shutter motor is fed from a Field Effect Transistor (FET) via pin 10 of the headlight connector (I haven't verified the pin number yet).

The problem is that, doing a bit more research, you can't just tap into that wire and connect to a relay as it has all sorts of odd effects including, so I gather, back emf spikes which could damage the FET when the relay switches off. This can be fixed with a diode but so far I have only found theoretical circuit info, nothing specific to this particular issue so, unless I can find details of a working setup, I will not attempt any experimentation at the moment.

As before, if anyone has succesfully acheived this then details would be gratefully received otherwise I will feedback any info I can find as and when.

Thanks for the comments so far and fingers crossed!

What Nodge said, your relay won't damage the FET circuit if you put a diode across it. I'm an electronics engineer in my day job and we run relays off FETs all the time. It basically looks like this (borrowing someone else's diagram)






The FET at the bottom and the resistors are in the car electronics module, switching the negative side of the circuit. You add your relay coil as shown at the top, put a diode across it with the bar to the positive side.

Apologies for the delay in responding. Life gets in the way sometimes.

Thanks Nodge and congoblue. That seems like a possible answer.

I have identified the two wires going to the shutter inside the headlamp unit and now need to trace these back through the multi pin socket (they are all black wires inside the unit). I have ordered a relay with built in diode so will give it a go and report back.

Just to confirm my understanding, With headlights on dipped beam I should be seeing a permanent positive feed to the shutter coil and the other wire would go roughly 12v negative when I switch to main beam and the shutter should operate. I then wire in my new relay in parallel with the shutter coil with the bar on the diode on the positive side of the new relay coil? Yes?

Thanks.

I think the shutter is activated for full beam and is in its idle position for dipped, but I might be wrong.

When the shutter is inactive you'll see 12V on both wires.
When the shutter is active you'll see 12V on one wire and 0V on the other.

The 0V wire is the one you want. Wire your relay between 12V and this wire.

Thanks congoblue. Yes, I believe the shutter operates when main beam is selected so if it fails, it fails on dip beam.

Thanks also for the additional info. It’s been many years since I did any electronic theory at night school!

Ok. A bit further along the track and hopefully I can get the final pieces for the jigsaw!

Got old multimeter out this afternoon with the following results (working on the front left hand headlamp) :

The shutter coil is fed by one red wire and one black wire (this may not be relevant).

These connect to two black wires inside the headlamp unit, one of which (the one connected to the red shutter wire) goes to pin 10 of the multi connector and subsequently to a grey/brown wire in the headlamp loom. The other goes to pin 12 of the multi connector and subsequently to a black/yellow cable in the loom. Amazingly this aligns with the wiring diagram I have (the black/yellow being ‘ground’).

Connecting the positive multimeter lead to battery positive the following are the results:

Shutter passive
Grey/brown. 12.15v
Black/yellow. 12.15v

Shutter active
Grey/brown. 0.2v
Black/yellow. 11.79v

Congoblue - your last post advises connecting my new relay (with inbuilt diode) across the 0v wire (grey/brown in this case) and positive.

Can I ask, do my latest investigations confirm this and also could you advise whether this should be a separate (fused) positive feed and which side should the bar on the diode be (pos or neg feed)?

Apologies if I am being a bit dense but I don’t want to mess anything up!

If successful I will put up details of the process in a separate thread as it may be useful to others.

Thanks.

Yes that sounds correct. So the grey/brown wire is being switched to ground by the control module.

You could just connect the relay across the 2 wires rather than looking for another 12V feed. Diode bar to the permanent 12V wire (so it's reversed - this is to catch the spike the relay coil gives out when power is removed).

Perfect! Thank you congoblue. Can’t get to it for a couple of days but will report progress.

Cheers,

Chris.

Hi All,

I started to have another look at the task this morning and it set me thinking.

When I described the voltage readings i reported earlier I should have perhaps made it clearer.

Because I had the pos lead of the multimeter connected to the pos battery terminal, the voltages I described were negative ones (this is where I perhaps should have made it clearer).

This morning, I connected the neg lead of the multimeter to neg battery terminal (ie. ground) with the headlight connected and got the following :

Shutter passive
Black/Yellow - 0v +
Grey/Brown - 0.02v +

Shutter active
Black/Yellow - 0.04v +
Grey/Brown - 11.6v +

so I believe that the shutter is being switched to (approx) 12v positive when activated. The Black/Yellow remains grounded.

The plan therefore is still to connect the relay across the Grey/Brown and Black/Yellow wires with the bar on the diode connected to the Grey/Brown side.

Does this sound like a plan?

Thanks,

Chris.