Parking sensor wiring help please

[monopoly]

Hi all,

Firstly to say hello - I'm a previous forum member returning to the forum having owned two MK1 Leons in the past, but having had a break from SEAT for a few years. Just picked up a MK3 SE 1.2TSI which I'm really loving and it's great to be back in a Leon.

My car doesn't have parking sensors and I'm about to start fitting them myself. I've done this before on several cars so am fairly confident but I'm looking for some help on the wire colouring on the MK3 Leon.

I've uncovered the boot hatch loom just under the rear headlining and also identified the reverse light positive feed at the bulb holder.

The problem I have is that whilst the GREY/WHITE wire is obviously the + reverse light feed at the bulb holder, it's the one colour which doesn't appear in the loom heading into the boot hatch!

On further investigation, I noticed that the reverse light only functions when the boot hatch is shut, so it would make sense that the GREY/WHITE is a combined feed from the reverse signal, via the boot latch.

To save me popping off all the hatch trim to test all the wires at the latch end, does anyone know which colour in the headlining loom is the reverse signal please?!?

Many thanks in advance

 

[dw911]

Hi all,

Firstly to say hello - I'm a previous forum member returning to the forum having owned two MK1 Leons in the past, but having had a break from SEAT for a few years. Just picked up a MK3 SE 1.2TSI which I'm really loving and it's great to be back in a Leon.

My car doesn't have parking sensors and I'm about to start fitting them myself. I've done this before on several cars so am fairly confident but I'm looking for some help on the wire colouring on the MK3 Leon.

I've uncovered the boot hatch loom just under the rear headlining and also identified the reverse light positive feed at the bulb holder.

The problem I have is that whilst the GREY/WHITE wire is obviously the + reverse light feed at the bulb holder, it's the one colour which doesn't appear in the loom heading into the boot hatch!

On further investigation, I noticed that the reverse light only functions when the boot hatch is shut, so it would make sense that the GREY/WHITE is a combined feed from the reverse signal, via the boot latch.

To save me popping off all the hatch trim to test all the wires at the latch end, does anyone know which colour in the headlining loom is the reverse signal please?!?

Many thanks in advance

Hi monopoly, the wire your looking for is black/blue
hope that helps

 

[monopoly]

Thanks for the reply. I've checked this morning and there's two black/blue wires in the headlining loom. Do you know if they're the same purpose? (You'd struggle to tell them apart as they're the same gauge too).

 

[dw911]

Can't say for certain if both of them are for the reverse circuit ,am just curious why you would be looking to tap into the reverse circuit in the roof lining when the parking sensors fit in the bumper.
I picked up the wire where it runs along the door cills and up over the rear wheel arch

 

[monopoly]

That was just the first place I followed the loom back to after it leaves the rubber connector with the boot hatch. I do have the rear seat side trim off now though and can see the loom as you mention, running up over the wheel arch, branching to the rear lights and into the headlining. You're right - it will be easier to pick up there.

Surely the two wires of the same colour must be for the same purpose. I'm going to try and get access to ELSAWIN to find a wiring diagram if possible, or worst case try both blue/black wires!

 

[dw911]

That makes sense you traced the wire back from the boot hatch

Got a rough idea for the reason for two wires the same colour in the headlining, but probably better to splice into the loom by the wheel arch now you have easy access with the trim removed

If you don't mind can u post up what it shows regarding the two black/blue wires in the headlining if you look it up in wiring diagram

 

[monopoly]

Will do! I got impatient this evening and went for it on the blue/black wires. As is sod's law, it was the 2nd one I stripped so I've still no idea what the other one might be for.

All's well that end's well though - I have a working reverse feed for the sensors and can move on to the scary part of removing the bumper and fitting them! Thanks again.

If I can get a wiring diagram, I will post up the colours.

 

[Orbiter]

Will do! I got impatient this evening and went for it on the blue/black wires. As is sod's law, it was the 2nd one I stripped so I've still no idea what the other one might be for.

All's well that end's well though - I have a working reverse feed for the sensors and can move on to the scary part of removing the bumper and fitting them! Thanks again.

If I can get a wiring diagram, I will post up the colours.

Good luck with all this, I was thinking of doing similar myself so when you have finished I would be very grateful if you could post any hints and tips including getting the rear bumper off. I think someone mentioned you can leave the bumper in situ and just take the rear under bumper panel off, drill the bumper,feed the sensor wires through the holes and into the boot etc. This would avoid scratching the bumper by accidentally damaging it whilst removing/replacing but perhaps may make it more difficult to position the wiring etc?

Also, which rear wheel arch is the reversing light wire, i.e nearside or LH driver side?
Thanks

 

[monopoly]

Good luck with all this, I was thinking of doing similar myself so when you have finished I would be very grateful if you could post any hints and tips including getting the rear bumper off. I think someone mentioned you can leave the bumper in situ and just take the rear under bumper panel off, drill the bumper,feed the sensor wires through the holes and into the boot etc. This would avoid scratching the bumper by accidentally damaging it whilst removing/replacing but perhaps may make it more difficult to position the wiring etc?

Also, which rear wheel arch is the reversing light wire, i.e nearside or LH driver side?
Thanks

Thanks. Yes, I'll try and write up the whole lot when I get it finished. I'm not sure I can avoid removing the bumper as I intend to fit flush-fitting sensors which have to be fixed with adhesive collars on the inside of the bumper.

The loom containing the reverse wire runs up over the wheel arch on the near side (passenger side). You need to remove the plastic trim at the side of the rear seat to gain access to it. Just a bit further up inside the body on the same side, there is a convenient earthing point, so it's fairly easy to get the connections you need.

 

[monopoly]

Quick update on this... the other blue/black cable is the rear fog light.

From the diagram it appears that one is 0.5mm gauge (reverse) and the other (fog) is 1.0mm gauge but they look the same to me!

 

[dw911]

Quick update on this... the other blue/black cable is the rear fog light.

From the diagram it appears that one is 0.5mm gauge (reverse) and the other (fog) is 1.0mm gauge but they look the same to me!

Cool, thanks for the update, handy to know

 

[monopoly]

Okay so my sensors are all fitted and working now. I'm pleased with the result and it wasn't too hard. I took plenty of photos as I went so am intending to do a write up on here but unfortunately can't at the moment as my post count is still less than 15

 

[Orbiter]

Okay so my sensors are all fitted and working now. I'm pleased with the result and it wasn't too hard. I took plenty of photos as I went so am intending to do a write up on here but unfortunately can't at the moment as my post count is still less than 15

Thats great, looking forward to the write-up. Btw where did you get the flush fitting sensors from?

 

[monopoly]

I got them from....

 

[monopoly]

...eBay. Cobra R0394 sensors which were about £75.

 

[monopoly]

But I also had to buy a sheet metal punch to make the holes, and the primer, paint and lacquer to spray the sensors. So I think that made the cost about £110 all-in. I know there's some local fitters who will do it for you for about £180-£200 so I guess it depends how much you enjoy doing the project yourself as the saving isn't huge....but I was keen to DIY

 

[monopoly]

As mentioned, the write up is now here

 

[JoeBloggs]

Holy thread resurrection Batman! I can confirm this is still the case on the 2018 Cupra ST. That grey wire with a white stripe on the back on the light unit somehow changes to a black wire with a blue stripe by the time it joins the rest of the loom and heads off over the wheel arch. Many thanks dw911 you certainly saved me a lot of time searching for it after I tested the grey/white and it was showing 0.7v some kind of bus signal?

Now onto my question, I'm actually doing this for towbar electrics so I have the same issue on the other side for the fog light wire... Does anybody know what the black/blue fog light wire changes to by the time it's joining the rest of the loom? I'm assuming it would be going over the right wheel arch but there's no black/blue wire in the bundle I'd expect it to be in!

Thanks for reading

 

[JoeBloggs]

I think I have found the answer to this now.

The grey wire with a white stripe coming from the brake light becomes a black wire with a blue stripe as above.

Then the opposite is true for the fog light the other side; it's a black wire with a blue stripe from the light that then becomes a grey wire with a white stripe.

I'd be willing to bet that it's the result of a left hand drive / right hand drive alternative configuration where the reversing light and fog light are swapped over.

I hope this post helps somebody else fitting towbar electronics in future.