Octavia III - Main beam wiring query?

[CFBScout]

Hi all, hoping someone can help me please. I am installing equipment to my Octy as it is used as a private ambulance response vehicle and I'm stuck on the headlight flasher unit.

 

I unplugged the connector at the back of the lamp unit (halogens) and used my multi-meter to try and find the dip or main beam feeds. However, it seems all the feeds across the top of the plug are live even with the lights off. I am therefore presuming it is a negative switched setup which is a pain.

 

Does anyone have a wiring diagram to confirm this and also help identify which earth serves the main or dipped beams please?

 

Many thanks in advance.

[encephalopathy]

i'd be interested in advice if you are fitting a siren - what have you bought/how did you wire it up etc

i think there is a spare grommet in the octavia behind the battery that can be used to conduit into the car from the engine bay

 

as for lights i have a unit that mounts inside the front windscreen power via the cigarette socket 

[CFBScout]

I have a full covert lights/siren solution sourced via my NHS work. All in and working except the headlight flasher which is frustrating as I expected that to be the easy part. The flasher unit switches out a +'ve feed so I think I will need to use 2 x relays to switch the earth to the lights instead which is a real faff

[brettikivi]

I'm reasonably sure it's a switched earth.

 

- Bret

[CFBScout]

Hmm, the plot thickens. I tested with my multimeter and the full top row of connectors are live at all times with ignition on, the outer 2 are around 10v while the inner 4 are 12.8v. All the earth connectors along the bottom row are giving an earth even with the lights off.

 

I'm baffled - anyone shed any 'light' on my problem? Is it some sort of canbus controlled system with a switching board inside the headlamp units perhaps?

 

 

[MrAdamwood]

Send xpower a message this sounds right up his street! He's done a lot of mods to his lighting system. 

[andyvee]

It is most definitely CANBUS controlled, and if you continue to mess about you run the risk of damaging your BCM, which is costly.

 

You can't wire additional items in this way, the voltage drop / resistance / impedance is monitored by the BCM.

 

If I was doing this, I would consider taking a feed from the other side of the BCM, i.e. the switch side to switch a relay that is powered off of a spare live or switched live location in the fusebox.

[xpower]

A few things:

1) its live switched not earth switched, does your flasher unit switch to earth or switch on a live.

2) on you car the HALOGEN bulbs are not part of the CAN / CANBUS or any other network. They are switched live(s) directly from the 09 CCM, the CCM is on the CAN but the headlights themselves aren't.

3) Assuming your unit is live switched, when connecting to the headlight feeds it will back power the CCM and may generate a fault code for headlight bulb.

4) this can be fixed by putting a diode between the CCM and before you splice into the wire, this will prevent any back feeding and back EMF caused by the unit.

5) issue is that that diode will get HOT, potentially very hot and it will be at around 4-5 amps @ 12v.

6) I will see if I can locate a wiring diagram for you

 

[CFBScout]

Thanks, I'm usually reasonably good with auto electrics but can't figure out why the plug for the light cluster is live on all the main pins even when the lights are off? I would have expected to see 12v present at the separate pins as the switch is moved through side, dip and main beam but they are all live???

[xpower]

They aren't all live - the voltage you are seeing with your multimeter is the CCM applying voltage down the wire to do a bulb check.

[xpower]

What's you reg?

it appears there may have been a change in wiring colours at certain years on the mk3

[CFBScout]

Ah I see, so my flasher unit switches 12v, if I add the diode to prevent the feedback in theory that should work?

 

mine is a 66 plate (Jan 17)

[xpower]

Engine? The reg is easier - PM me if you want with it so I can be 100%

[xpower]

I don't have the wiring diagram for the 2016 / 2017 models, it might be the same please check the wiring colours.

I think if it was me I may use the feed to the dip or main (which ever you choose) to trigger a relay to power the bulb.  And then use your box to also trigger that same relay.

You would loose bulb warnings and the errors would have to be coded out with VCDS or similar.

Rather that than the diode method, they will get quite hot especially in the winter when the headlights are on a lot.

 

If you don't do that you could look at the main beam switch wiring and trigger that instead but the lights wont flash alternatively side to side then

 

 

[encephalopathy]

22 hours ago, CFBScout said:

I have a full covert lights/siren solution sourced via my NHS work. All in and working except the headlight flasher which is frustrating as I expected that to be the easy part. The flasher unit switches out a +'ve feed so I think I will need to use 2 x relays to switch the earth to the lights instead which is a real faff

Could you send me the details as I am looking for the same setup with green lights/siren/controller

thanks

[CFBScout]

Well I'm not too sure I'm going to put 12v down the main beam from my flasher unit for fear of causing canbus issues or frying something. Still can't quite fathom why the meter shows +12v feed present but the lamps are not lit??

 

Anyone know if the front fogs are a simpler setup?