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How to make your 12v accessory socket permanently live

dw911

Active Member
Mar 30, 2013
1,038
4
I have a couple of things plugged into the 12 volt socket in front off the armrest
Now I've found it a bit of an inconvenience that it's only live with the ignition on
So I thought I'd see if I could make it permanently live and not controlled by the ignition, but I didn't really want to chop the wiring about

This is how I did in case anyone else wants to do the same

You need to pull down the glovebox (it's explained in the manual) to reveal the fuse box, in the middle of the fuse box you will see a yellow 20 amp blade fuse (location f40)
You will notice it sits a slight bit lower than the green 30 amp fuse to its left.
Remove the yellow 20 amp fuse,now move it up slightly until it is parallel with the green fuse next to it, push the fuse back in.

Your 12 volt accessories socket is now permanently live

Best of all its easily reversed if you change your mind

Now I was concerned that I may accidentally leave something plugged in and flatten the battery
But that can't happen as the battery monitoring system on the car will still shut it off if the battery starts to get low to leave enough power in the battery to still start the car

Anyway it may be of use to some of you

Cheers
 
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Marve

Active Member
Apr 20, 2013
191
9
Wow, wow, wow... You, sir, have pretty much just saved my life!

I have a dashcam hard wired in that piggy backs from the F40 fuse socket and after messing about with it recently, I couldn't for the life of me work out why it was now always on whereas before it would shut off with the ignition.

You have just solved my mystery crisis, I must have put the fuse back inline with the rest now, I need to drop it again!!

Thanks so much :)
 

TMO

Active Member
Feb 15, 2008
192
1
Stafford, Staffs
Thanks alot for this, my current Octavia did this from the factory and I also find it useful for charging my phone when I'm sitting in the car and its not running so I'll be definitely doing this on my Cupra when it arrives.
 

dw911

Active Member
Mar 30, 2013
1,038
4
Brilliant idea there. That is an annoying thing when I can't charge my phone whilst sitting there with the engine off.
Wow, wow, wow... You, sir, have pretty much just saved my life!

I have a dashcam hard wired in that piggy backs from the F40 fuse socket and after messing about with it recently, I couldn't for the life of me work out why it was now always on whereas before it would shut off with the ignition.

You have just solved my mystery crisis, I must have put the fuse back inline with the rest now, I need to drop it again!!

Thanks so much :)
Thanks alot for this, my current Octavia did this from the factory and I also find it useful for charging my phone when I'm sitting in the car and its not running so I'll be definitely doing this on my Cupra when it arrives.

No problem, glad you found the guide useful:)
 

BigfatPaulie

Active Member
Sep 18, 2013
194
3
Nottingham
Was thinking about this very thing last night !!!!! I was going to hack the wiring... but seems its not necessary !!!! BIG Thanks ;-)


EDIT..
can't find the fusebox:-( or find anything about it in the manual.
..... Arrrr, found it with a little force ;-) I guess you're supposed to press the catches? haahahha
 
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dw911

Active Member
Mar 30, 2013
1,038
4
Great just what I wanted. Thanks very much
Was thinking about this very thing last night !!!!! I was going to hack the wiring... but seems its not necessary !!!! BIG Thanks ;-)


EDIT..
can't find the fusebox:-( or find anything about it in the manual.
..... Arrrr, found it with a little force ;-) I guess you're supposed to press the catches? haahahha
:) glad it was useful

Just to add, since I did this, two days later the fuse blew (it may have been my house keys falling in to the socket in the centre console and shorting it out, but can't be sure)
Anyway I change the fuse from a 20 amp to a 25 amp and it hasn't happened again (the cabling and the socket can handle up to 30 amps for small periods)
 
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Branta

Active Member
Feb 22, 2015
36
0
Nottinghamshire
This is a great discovery, thanks for the tip.

But how sure are you about:
.... the battery monitoring system on the car will still shut it off ....
My expectation of an "always live" accessory socket is that there is only a fuse between the socket and the battery. It's a popular option to plug a battery charger in at the accessory socket. I like to do that because I sometimes work overseas for up to six weeks at a time. In the winter it's nice to have the car start when I get home again. Not sure I fancy doing that if there is shut-off circuitry involved, unless I'm satisfied it's simply relay contacts.

Now how would I find a wiring diagram ? Haynes have a manual for the NASA Space Shuttle, but not for a SEAT Leon (or even the current Golf).
 

BigfatPaulie

Active Member
Sep 18, 2013
194
3
Nottingham
...well, Ive left things charging overnight, and its not turned off !!!!

Doubt very much that the charger socket is controlled in ANY way, other than a fuse.
 

dw911

Active Member
Mar 30, 2013
1,038
4
This is a great discovery, thanks for the tip.

But how sure are you about:


My expectation of an "always live" accessory socket is that there is only a fuse between the socket and the battery. It's a popular option to plug a battery charger in at the accessory socket. I like to do that because I sometimes work overseas for up to six weeks at a time. In the winter it's nice to have the car start when I get home again. Not sure I fancy doing that if there is shut-off circuitry involved, unless I'm satisfied it's simply relay contacts.

Now how would I find a wiring diagram ? Haynes have a manual for the NASA Space Shuttle, but not for a SEAT Leon (or even the current Golf).
Very sure,
it's not like the old days where a car had a large gauge wire to the fuse box, then lots of smaller wires run through fuses to feed various accessories and equipment in the car and that was it
Nowadays most of a cars electrical system is controlled by a battery management system or similar, you only have to connect the VCDS diagnostic kit to see how everything is now run through ecu's (there's even something about it in the manual).
But basically the car will do its best to shut down non critical electrical parts of the car in a effort to preserve enough power in the car to allow the car to still start.
That's why on a lot of new cars if you fit a new battery u need to program the battery or the battery code into the car with the manufacturers diagnostic tool so it knows how many Ah the battery has in it.
On my other car it even puts the alarm and central locking into deep sleep mode after a few weeks and you have to use the key in the door lock to wake it up ( obviously that part doesn't apply to the leon, as it has no door locks)

As for an electrical wiring diagram, unless you can find one on line or get a copy of the factory dealer workshop disk ( I think vag no longer send out cds/disc's with it on, it's all on line and the dealer's etc pay a fee to use it on their workshop diagnostic tables/computers and it's password protected)
The only place I have got them for newer cars is by having a chat with one of the mechanics at the relevant dealer and asking them nicely to print out the relevant pages
 

dw911

Active Member
Mar 30, 2013
1,038
4
...well, Ive left things charging overnight, and its not turned off !!!!

Doubt very much that the charger socket is controlled in ANY way, other than a fuse.

It won't overnight, unless you have plugged you toaster in to it overnight ;)

Most things by their very nature that are plugged into the accessory socket are only drawing in the mAh range, the car has a huge battery with a large AH capacity, it would take weeks to run/discharge the battery down enough for the car to shut down the accessory socket

To put it in to perspective, draining your leon battery by charging say your phone from it it, is akin to draining your swimming pool using a tea cup.
Neither will happen overnight ☺
 
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Seastormer

Cupra 280/CBF1000
Apr 25, 2014
4,026
274
64
Edinburgh (Scotland)
Very sure,
it's not like the old days where a car had a large gauge wire to the fuse box, then lots of smaller wires run through fuses to feed various accessories and equipment in the car and that was it
Nowadays most of a cars electrical system is controlled by a battery management system or similar, you only have to connect the VCDS diagnostic kit to see how everything is now run through ecu's (there's even something about it in the manual).
But basically the car will do its best to shut down non critical electrical parts of the car in a effort to preserve enough power in the car to allow the car to still start.
That's why on a lot of new cars if you fit a new battery u need to program the battery or the battery code into the car with the manufacturers diagnostic tool so it knows how many Ah the battery has in it.
On my other car it even puts the alarm and central locking into deep sleep mode after a few weeks and you have to use the key in the door lock to wake it up ( obviously that part doesn't apply to the leon, as it has no door locks)

As for an electrical wiring diagram, unless you can find one on line or get a copy of the factory dealer workshop disk ( I think vag no longer send out cds/disc's with it on, it's all on line and the dealer's etc pay a fee to use it on their workshop diagnostic tables/computers and it's password protected)
The only place I have got them for newer cars is by having a chat with one of the mechanics at the relevant dealer and asking them nicely to print out the relevant pages
It does have a door lock, it's hidden by a plastic cover with a little hole in it (on the underside) for you to use your key to prise off.
 

dephead2004

Active Member
Aug 3, 2013
923
9
Very sure,
it's not like the old days where a car had a large gauge wire to the fuse box, then lots of smaller wires run through fuses to feed various accessories and equipment in the car and that was it
Nowadays most of a cars electrical system is controlled by a battery management system or similar, you only have to connect the VCDS diagnostic kit to see how everything is now run through ecu's (there's even something about it in the manual).
But basically the car will do its best to shut down non critical electrical parts of the car in a effort to preserve enough power in the car to allow the car to still start.
That's why on a lot of new cars if you fit a new battery u need to program the battery or the battery code into the car with the manufacturers diagnostic tool so it knows how many Ah the battery has in it.
On my other car it even puts the alarm and central locking into deep sleep mode after a few weeks and you have to use the key in the door lock to wake it up ( obviously that part doesn't apply to the leon, as it has no door locks)

As for an electrical wiring diagram, unless you can find one on line or get a copy of the factory dealer workshop disk ( I think vag no longer send out cds/disc's with it on, it's all on line and the dealer's etc pay a fee to use it on their workshop diagnostic tables/computers and it's password protected)
The only place I have got them for newer cars is by having a chat with one of the mechanics at the relevant dealer and asking them nicely to print out the relevant pages
I bought a CD set from eBay for our leons. It has complete workshop manual, wiring diagrams and other goodies. Defo worth the 15 I paid for it.
 

Branta

Active Member
Feb 22, 2015
36
0
Nottinghamshire
.... it's not like the old days where a car had a large gauge wire to the fuse box, then lots of smaller wires run through fuses to feed various accessories and equipment in the car and that was it
Nowadays most of a cars electrical system is controlled by a battery management system or similar, you only have to connect the VCDS diagnostic kit to see how everything is now run through ecu's (there's even something about it in the manual)....
My guess (and it's only a guess) is that by plugging the accessory socket fuse in at the "alternate" position you are bypassing the clever control features as well.

By the way, the charger that I leave plugged into my Passat if I'm working overseas during the winter months is ASIN: B004ZWV1JI on Amazon UK (sorry, I'm not allowed to post links yet, use the ASIN code in an Amazon search), it's clever enough to wind itself down to a trickle rather than make the battery "gas" like an old charger would. And it plugs into the accessory socket using the adapter ASIN: B0016LA5O8. There are no warnings about the possibility of damage when charging through the accessory socket, so I guess I'll just try it !

Postscript: having thought about it some more !

Even if the accessory socket is controlled by electronics, the actual switch will be either relay contacts or a P-channel MOSFET.

If it's a relay it won't mind passing current in the reverse direction. If it's a Power MOSFET there will be a reverse-protection schottky diode built into it, which will pass the reverse current. These protection diodes are typically rated higher than the FET itself, though there will be a greater volt drop which means there will be more power dissipation. But the charger won't try to push 20A, it's rated at 5A and in fact under the type of regular use to which I will put it, it'll deliver 5A only for a few seconds, if at all.

So I have stopped worrying about plugging-in the charger at the accessory socket as a winter precaution.

But if I ever find myself with a really flat battery, then I'll lift the bonnet and connect the charger in a more conventional way !
 
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