Switched Live for Parking Sensors

[GrahamM]

As I'm not very good at judging distances, I'm going to install front and rear parking sensors on my Mark II 2012

 

I've bought a kit, but there are four connections:

 

Black: -12V Ground

Blue: +12V Brake light

Yellow: +12V Reversing light

Red: +12V Accessory line

 

It's the last one, Red, that's giving me problems as it needs to go to a switched live, ie one that's only active when the ignition is turned on, so the system isn't drawing power with the ignition off.

 

I've searched around in here and there's mentions of eg a connection to the radio, but is there anywhere in the boot area that I can connect to instead to avoid having to run an extra wire?

 

[26DIPP]

Normally the PDC / parking aid is supplied from fuse 9 - 5A.

 

The fuel pump under the rear seat is the closest user in the back I can think of. But if the PDC ever created a fault and blew the fuse troubleshooting would be a nightmare.

[Jocko]

The PCD should sit in the RH side of the boot. Although not fitted, I would check and see if the wiring for it is there. A lot of times they use a standard harness in cars then connect up what is required and leave dangling what isn't. It is worth a look.

[GrahamM]

17 minutes ago, Jocko said:

 I would check and see if the wiring for it is there.

That's an interesting thought!

I'll have a check around and see what I can find.

[KeithCheetham]

Are these the type with just a sounder or with a visual display of distance on the dash, and is it a rear only or rear plus front kit? May sound daft, but it may be worth wiring up temporarily with the blue, yellow and red all connected to the + reversing light cable and the ground to the - reversing light cable. I cannot think of a reason for connecting a brake light wire up. I understand that some cars with CANBUS may have needed a relay with a feed from a 12V as it is understood only 5V passes down a line, but how this operates a 12v revering light bulb is strange. I have fitted a few sets to Mk1 Fabias, my current 58 plate Fabia and my daughters 61 plate Polo and they have all only had/needed 2 wires connecting to the reversing light powering the sensors and its control box.

Update - Just seen an advert on Ebay 8 Sensors Parking Reverse Front and Rear Car Parking Sensors Display Buzzer Kit | eBay showing 8 sensor system, also mentioning brake light connection but still unsure why. NOTE that in the pictures in the advert there is a red box containing the text shown in the attachment. May be worth connecting sensors to control box before fitting, laying sensors out to final positions of front and rear, wiring to positive and negative on car or spare battery and just testing operation before you start drilling bumpers and laying out rear (control box position) to front sensor wiring inside car.

Edited 23 December, 2023 by KeithCheetham

[GrahamM]

22 minutes ago, KeithCheetham said:

I cannot think of a reason for connecting a brake light wire up.

The control box is permanently "on" when the ignition is on, hence why it needs a switched live,

The front sensors are triggered by the brake light coming on and stay active for about 20 seconds, but the counter restarts if you press the brake again, the rear sensors only activate when you're in reverse and the light is on.

 

The display has a beeper and a distance gauge, but also sections of LEDs to each side of the distance display that light up according to which sensors are detecting, so even if you're reversing, if the front LEDs light, you know that your front bumper is getting close to an object.

 

BTW I've already checked the system using a spare motorbike battery and all the sensors work OK.

[GrahamM]

These are the sensors I've bought: https://www.amazon.co.uk/dp/B00X9UCN8K/ref=pe_27063361_485629781_TE_item
 

Attached is a pick of the instructions, Section A, the 6-8 Sensor System is the relevant one.

[Breezy_Pete]

Rear wiper power feed tends to be ignition switched 12V.

 

[GrahamM]

1 hour ago, Breezy_Pete said:

Rear wiper power feed tends to be ignition switched 12V.

 

True, but there would only be power if the wiper is switched on 🙂

[Breezy_Pete]

Not true.

[Breezy_Pete]

You'll find this black wire in position 3 of a 10-way connector pair on the left side of the luggage compartment. Other wires cause the wiper and rear washer to activate in response to stalk inputs.

Test it with and without ignition switched on. 🙂

[KeithCheetham]

14 hours ago, GrahamM said:

These are the sensors I've bought: https://www.amazon.co.uk/dp/B00X9UCN8K/ref=pe_27063361_485629781_TE_item
 

Attached is a pick of the instructions, Section A, the 6-8 Sensor System is the relevant one.

Thinking that this may be based on a brake light bulb having a 12v supplied constantly with the earth (-ve) being applied through the brake light switch when the pedal is actuated to allow the bulb to light up. Breezy_Pete may be able to advise if this is applicable on the Fabia.

[Breezy_Pete]

No, brake lights are only given 12V when pedal is pushed.

Reasoning for the connection is explained in one of Graham's posts above. To briefly enable front sensors.

[ApertureS]

On 22/12/2023 at 18:21, Jocko said:

The PCD should sit in the RH side of the boot. Although not fitted, I would check and see if the wiring for it is there. A lot of times they use a standard harness in cars then connect up what is required and leave dangling what isn't. It is worth a look.

Not a chance will the wiring be there, VW group havent ever done a single harnesses. All harnesses in this century are ordered against a VIN number and are made to order for that specific car. 

 

 

[GrahamM]

3 hours ago, Breezy_Pete said:

You'll find this black wire in position 3 of a 10-way connector pair on the left side of the luggage compartment. Other wires cause the wiper and rear washer to activate in response to stalk inputs.

Test it with and without ignition switched on. 🙂

 

Ok, thanks.

 

Before I start taking bits off, this video (starts at 4'36) shows a guy fitting sensors and refers to the "boot wiring plug". Is that the one I'm looking for?

https://youtu.be/pTAC1XrKXqc?feature=shared&t=286

 

Also, where you say "Position 3" is there a way to know which is position 3? Are they numbered? I don't want to get the wrong one...!

[Breezy_Pete]

Quite likely that's it, yes, but don't know from personal experience on a mk2 Fabia.

Connectors do tend to have pins numbered, but there's a decent chance it's the only black wire.

As long as the connector has a black wire, it's probably an ignition switched feed.*

 

Edit

* No, actually there's a thicker black wire going to the rear screen heater on pin 1, white in the mating part of the connector pair. Don't use that one.

 

 

Edited 24 December, 2023 by Breezy_Pete

[GrahamM]

8 minutes ago, Breezy_Pete said:

* No, actually there's a thicker black wire going to the rear screen heater on pin 1, white in the mating part of the connector pair. Don't use that one.

 

 

Noted, thanks.  That should help me figure out which end is which 🙂

I'll take a look at this in a couple of days when I've got the time...

[GrahamM]

For various reasons, including being busy, crap weather, being ill and simply not getting off my backside, I've not had a chance to look at this until now, except I've just found that the reversing light is not working, so there's no point in installing the sensors until I've sorted that.

 

I've checked the bulb and that's fine, so my next guess is either a fuse, faulty switch or duff wiring.

 

The fuse is the easiest to check, but I don't know where to find it.

 

Please can someone point me in the right direction? Mark II Skoda HTP 2012