Mk3 Fuse Box layout

[Chris Green]

The owner's manual is particularly useless on this subject, confining itself to the colour-coding of fuse ratings. I've two electrical problems at the moment.

1. Neither 12v accessory socket works, i.e. in cabin and in the boot.

2. Rear wiper motor not working (washers are OK)

It may well be that both problems are related to the same fuse but I'm having trouble getting a diagram. To save me a 40-mile round trip to a dealer, does anyone know where I can find the layout of the fuse box(es)?

 

[dw911]

Can't tell you the cigarette lighter /accessory socket fuse number off hand
But know it's the yellow fuse directly above the black relay with 645 written on it
its the yellow 20 amp one that is lower down that the others in the same row.
Anyway hope that helps

 

[Chris Green]

Many thanks, I'll go and have a look now.

UPDATE: I had a look at the 20 amp fuse and it was OK. However, I'd read elsewhere whilst 'googling' that moving it up 'half a position' so it's level with the 30 amp next to it, turns it into a permanent live socket, which mysteriously works so at least the wiring is OK. I'm no nearer finding out what's stopped the rear wiper working. Maybe they didn't blow at the same time, and I only noticed the wiper later. Still no idea which fuse could be for the rear wiper.

 

[Walone]

Many thanks, I'll go and have a look now.

UPDATE: I had a look at the 20 amp fuse and it was OK. However, I'd read elsewhere whilst 'googling' that moving it up 'half a position' so it's level with the 30 amp next to it, turns it into a permanent live socket, which mysteriously works so at least the wiring is OK. I'm no nearer finding out what's stopped the rear wiper working. Maybe they didn't blow at the same time, and I only noticed the wiper later. Still no idea which fuse could be for the rear wiper.

If it's any help the fuse for the 12v sockets is fuse number 40 (20amp) and the fuse for the rear wiper is fuse number 47 (15amp)

 

[Chris Green]

Many thanks, I'll give that a try in the morning.

 

[Chris Green]

Still none the wiser although it transpires that the only problem with the rear wipers was that I'd put the fuse back into slot 48, not 47!

However, I gave in and took the car to my SEAT dealer in the end, who "changed a fuse", although I don't know which one.

I still have this odd quirk with the accessory socket - fuse 40 IS NOT BLOWN and yet in the 'switched position' nothing happens - it worked for a few minutes after leaving the garage but by the time I was home, I was back to square one.

OK, I'm prepared to admit that this points to a duff USB charger or maybe the lead so these'll be the subject of further testing with a multimeter but why does the LED on my charger still come on when I shift the fuse to the 'permanent position'. I'm getting the garage to ring me back to tell me just which fuse they DID change 'cos it sure as hell wasn't the 20amp in slot 40.

Done some testing on the 3 pins of slot 40.

Top pin (permanent live) to rim of cigar lighter = 12 volts.

Bottom pin (with ignition on) to rim of cigar lighter = dead.

Middle pin to centre of cigar lighter = continuity.

I'm beginning to wonder is there isn't some other fuse or relay in series with the ignition-on setting that I don't know about. Presumably it would have to be lower than 20 amps to blow first?

UPDATE: I was right, there is another fuse in line with the switched position for fuse 40. It's fuse 34 which is a mini-sized fused rated at 7.5 amps (very low surely?). replacing this (again!) has cured the problem as has throwing away all cheap nasty looking charging devices!

Maybe we should start a repository of Mk3 Leon fuses and what they do?

I'll kick it off.

26. Heated Seats - yellow 20 amps
34. Mini-fuse (brown) 7.5* amp linked to the switched position of Fuse 40 for 12 v Accessory sockets when switched. I.E if you overload the socket, this will be the first to blow, not No. 40.
40. 12v Accessory sockets (up= live, down =switched)
47. Rear wiper = 15 amp blue

*This seems unduly low as it sits in series with a 20amp fuse designed to handle two 10 amp accessory sockets.

 

[Walone]

I'm beginning to wonder is there isn't so other fuse or relay in series with the ignition-on setting that I don't know about. Presumably it would have to be lower than 20 amps to blow first?

UPDATE: I was right, there is another fuse in line with the switched position for fuse 40. It's fuse 34 which is a mini-sized fused rated at 7.5 amps (brown). replacing this (again!) has cured the problem as has throwing away all cheap nasty looking charging devices!

Maybe we should start a repository of Mk3 Leon fuses and what they do?

I'll kick it off.

26. Heated Seats - yellow 20 amps
34. Mini-fuse (brown) 7.5 amp linked to the switched position of Fuse 40 for 12 v Accessory sockets when switched. I.E if you overload the socket, this will be the first to blow, not No. 40.
40. 12v Accessory sockets (up= live, down =switched)
47. Rear wiper = 15 amp blue

It doesn't make sense to have a 7.5amp fuse in line with fuse 40 (20amp) as each 12v power socket has a maximum rating of 120watts (10amps) according to the owners manual.
Also it shows in the manual that there are 3 x 7.5amp fuses, 1 for the rear camera (if fitted), 1 for Parking Aid control unit and 1 for Reverse switch, Clima sensor and Electrochromic
mirror.

 

[Chris Green]

Not sure which owner manual you've got. Mine tells me nothing except which colour has which rating. No diagram, no list, nada.

I agree, and I wish I'd thought of taking a picture before fuses got changed. Up to a point, I'm not that worried as I only ever charge my phone from the socket, but yes, you'd have thought that the mini-fuse 34 should also be a 20 amp. If it continues to give trouble, I'll upgrade it.

 

[Walone]

Try this link for manuals, http://www.seat.com/owners/your-seat/manuals-offline.html choose your manual from the drop down list, fuses are listed on or around page 93.

Never fit a higher rated fuse than is originally fitted!

 

[Chris Green]

Try this link for manuals, (link removed) choose your manual from the drop down list, fuses are listed on or around page 93.

Never fit a higher rated fuse than is originally fitted!

Still no use I'm afraid. I've printed out pages 92 and 93 from a manual for a 2015 ST and it's largely right in agreement with my photo.

However, as you say, fuse 34 is shown as a 7.5 amp for the reverse switch, chroma mirror etc whereas on mine, it quite definitely shuts off the 12v socket if removed. Weird. It'll be interesting to see if it turns off the chroma mirror too.

The manual for my December 2014 ST shows nothing at all so this printout is now the best I've got with certain reservations.

 

[Walone]

Weather permitting I will take a look at mine tomorrow to see if pulling that fuse out stops the 12v sockets working.

 

[Chris Green]

Many thanks. It's pouring here!

Sent from my ONE A2003 using Tapatalk

 

[Walone]

Well I managed to get out to the car today and try the fuses, I pulled out fuse 34 (7.5amp) and sure enough both of the 12v power sockets went dead! The only thing I can think of is that fuse 34 also controls the windings of a relay which gives power to the 12v sockets, but I can't understand why this fuse blew!
Would be good to have a circuit diagram!

 

[dw911]

Well I managed to get out to the car today and try the fuses, I pulled out fuse 34 (7.5amp) and sure enough both of the 12v power sockets went dead! The only thing I can think of is that fuse 34 also controls the windings of a relay which gives power to the 12v sockets, but I can't understand why this fuse blew!
Would be good to have a circuit diagram!

Yes I think you could be right on that, would make sense as it would take load off the ignition switch circuit I. E a very low amp draw trigger circuit, rather than a possible 20 amp load.
What doesn't make sense is why it blew, as it its only a trigger for the relay, a short in the 12 volt power socket should only blow the 20 amp fuse, and not the 7.5 amp one, as it's separated from the 20 amp power socket circuit.
I know on my last leon mk3, I accidentally knocked my house keys in to the power socket whilst driving and it only blew the 20 amp fuse.
TBH though, until you posted I didn't know it had more than one fuse

 

[Chris Green]

Well, I'm glad I'm not imagining things! Fuse 34 powering a high amperage relay makes all kind of sense, but as you both say, what on earth makes it blow?

Sent from my ONE A2003 using Tapatalk

 

[Walone]

Well, I'm glad I'm not imagining things! Fuse 34 powering a high amperage relay makes all kind of sense, but as you both say, what on earth makes it blow?

Sent from my ONE A2003 using Tapatalk

Assuming it's still blowing but only occasionally I would try and rig up a light plugged into the front 12v socket so that you can see when the fuse blows and what you were doing at the time it blows.

 

[Chris Green]

Fuse 34 blew again, and as far as I can make out, I wasn't doing anything with the 12v socket this time - I'd used it the previous day to charge my phone. I only noticed at night when the self-dimming mirror didn't work, there being no green LED glowing on it.

Have now bought the official car charger for my phone just in case it was a dodgy combination of cheapo USB charger and lead.

Had an urgent need to keep my phone charged on a long journey so I shifted fuse 40 to the 'always on' position and changed the fuse 34 again and all seems to be well.

However, I'll be moving it back after a period just to see if the new charger has done the trick. It would be nice to know which relay it is that's powered via fuse 34 though just in case it's that which is faulty causing 34 to blow occasionally.

 

[martin j.]

If the 7.5a fuse is for the relay supplying the sockets(that is if I'm reading this right) keeps blowing, could the relay or the plug on it be faulty? Or in fact the fuse board?

 

[Chris Green]

I'm coming to that conclusion too. It doesn't make sense that the relay fuse blows but the 20 amp feed for the 12v sockets is OK.

If only I knew which relay it really is - there are a few variously marked 645 and 646 in the internal fuse box alone, unless of course one of the circuits listed as being served by fuse 34 has an intermittent fault. The book mentions the chroma mirror, the 'clima' sensor and the reversing switch.

Not sure about the last one - my reversing light still works with the fuse blown, although my car's an automatic so maybe the wiring is different.

 

[Hughes395]

I believe i am also having troubles with fuses... the rear lid release wont wont- when the button both in the car and on key fob is pressed no noise can be heard coming from the boot even when stood ear against it. so ive come to the conclusion that the fuse is gone as the boot can still be opened manually. any guidance on which fuse it is? here's hoping it is just a fuse and not the solenoid!