# Problem with fuses



## jiwawa (Jun 22, 2007)

Hi - I've a problem with the 12v electrics.

I bought a 12v extension lead like this to enable me to blow up the tyres on the offside of the van as the lead with the compressor isn't long enough. However, what I didn't realise was the compressor needed up to 12a whereas the extension lead would take up to 5a only. So it blew the fuse in the extension lead.

Hubby took the lead to the local garage and they fitted a new fuse. When I plugged it into the cigar lighter and tried again it did something to the van electrics so that the cigar lighter didn't work any more. When I took the extension plug apart I discovered they'd put in a 35a fuse!!

Anyway, I thought I just had to replace the 20a fuse behind the glove compartment which protects the cigar lighter; but that wasn't actually blown, though one of the legs was a bit bent. I did replace the fuse but it made no difference.

The internal cab light is also not working. And more importantly, neither is out alarm.

Any idea what might be wrong? The other 12v in the cab is working (ours is a Transit, 2007, and the 1 on top of the dash is intact; also the one in the habitation area is working.

The problem one worked with the phone charger, then blew with the extension lead in; I don't think I even had the compressor turned on at the time.

Any ideas?

Thanks,

JWW


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## twinky (Aug 11, 2008)

Are you saying the new extension lead blows a vehicle fuse when its used in the transits front outlet only? But when somethings used without the ext lead it doesnt blow a fuse in the same outlet?
If so it sounds like a short in the ext lead. 
The link goes to the 12A compressor. Which wont blow a 20A vehicle fuse!
I'm confusing myself now :lol: .


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## jiwawa (Jun 22, 2007)

I don't know if it's blown a fuse or not - it's certainly not blown the fuse protecting the cigar lighter (in the standard relay box according to the manual) but maybe it's blown something else in one of the other 3 fuse boxes, but I can't see anything there that seems relevant.

I had tried the extension lead in the habitation 12v socket and it blew the 10a fuse in the Elektroblok. I replaced that and could see it was working because my phone worked through it. 

I then tested the phone charger in the cigar lighter in the cab area - it worked. I pugged in the 12v extension lead and it blew something - the phone charger no longer worked in that socket.

My lights and indicators seem to be working ok but it's bit worrying that the alarm isn't.


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## time-traveller (Apr 23, 2007)

JWW said:


> Hi - I've a problem with the 12v electrics.
> 
> I bought a 12v extension lead like this to enable me to blow up the tyres on the offside of the van as the lead with the compressor isn't long enough. However, what I didn't realise was the compressor needed up to 12a whereas the extension lead would take up to 5a only. So it blew the fuse in the extension lead.
> 
> ...


Your link is for the compressor, not the extension lead


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## time-traveller (Apr 23, 2007)

JWW said:


> I don't know if it's blown a fuse or not - it's certainly not blown the fuse protecting the cigar lighter (in the standard relay box according to the manual) but maybe it's blown something else in one of the other 3 fuse boxes, but I can't see anything there that seems relevant.
> 
> I had tried the extension lead in the habitation 12v socket and it blew the 10a fuse in the Elektroblok. I replaced that and could see it was working because my phone worked through it.
> 
> ...


Why don't you put a meter across the terminals of the extension lead to see if there's a closed circuit  i.e. a short circuit


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## Fatalhud (Mar 3, 2006)

before you blow every fuse in the vehicle I would chuck the lead in the bin :wink:


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## time-traveller (Apr 23, 2007)

Fatalhud said:


> before you blow every fuse in the vehicle I would chuck the lead in the bin :wink:


Best idea ! :idea:


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## jamiealana (Nov 18, 2006)

*YOUR PROB WITH FUSES*

We had the same problem all we did was cut the end of the extension and fitted croc /clips straight to the battery prob solved


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## CliveMott (Mar 10, 2008)

The original 5 amp fuse was to protect the flimsy lead. Bin the lot and start again.

You would be better off connecting the compressor directly to the battery with a pair of crock clips if it takes meaningful amounts of amps.

C.


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## pippin (Nov 15, 2007)

It is a common misconception that fuses in plugs (mains and 12V) are to protect the appliance fitted to the other end.

Their primary purpose is to protect the wire in case the appliance develops a fault and draws more current than the cable can safely handle before melting or bursting into flames.


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## jiwawa (Jun 22, 2007)

You'll not be surprised to hear that I know nothing about electrics! I got the extension lead because the compressor wouldn't stretch to the off-side rear wheels. I have used it successfully (without the extension) to blow up the other tyres so it would seem it is the extension itself - I will bin as directed.



time-traveller said:


> Your link is for the compressor, not the extension lead


Sorry! - Here's the correct link



time-traveller said:


> Why don't you put a meter across the terminals of the extension lead to see if there's a closed circuit i.e. a short circuit


I think since I'm so 'electricity illiterate' I'll just go with the binning idea! But thanks for the advice.



jamiealana said:


> We had the same problem all we did was cut the end of the extension and fitted croc /clips straight to the battery prob solved


To reach the rear wheels I'm going to have to put some extra wire in there somehow. I'd prefer to keep the 12v end if possible - I hate working with the battery direct. Is it possible just to put in-line connectors, or whatever they're called to make the flex longer?

And can anyone suggest how I might troubleshoot why the alarm etc aren't working?

I appreciate the feedback.


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## CliveMott (Mar 10, 2008)

Perhaps its supplied by the same fuse as your *** lighter socket?

C.


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## jiwawa (Jun 22, 2007)

The one that the manual says protects the cigar lighter (20a fuse) hasn't actually blown. It had a slightly bent leg though, so I put a new one in anyway, but no difference.


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## BJT (Oct 31, 2008)

Never replace a blown fuse with one which is rated higher, unless in an emergency. As others have said it is to limit the current to the safe rating of both the cable and the appliance. If you put a higher rated fuse in as a replacement there are several possible results, none good. You can overload the cable if there is a short circuit and melt it, you can damage other bits of kit which may be attached to the same circuit, you can blow another fuse elsewhere in the circuit as some wires are used in more than one circuit! You will need to get a circuit diagram for the vehicle, and as there are a myriad of versions of any basic vehicle the options it will include are mind boggling, so you need someone experienced in reading and understanding the perishing things to trace where to look for blown fuses and or circuit damage.
you have experienced the perils of taking an electrical fault to a 'mechanic' when you need an auto electrician. Chuck the 5a rated extension lead in the bin. Find a decent auto electrician and get him to sort out your problem in the van circuits and make you up a lead to suit your compressor. He will probably have to install a supplementary circuit with a suitable socket outlet for the load, and a fuse in the circuit as well.
Alternatively, and if you are competent to do it:-
A useful supplier for auto electrical bits is Auto Electric supplies ltd. Web site autoelectric supplies.co.uk, they are in Tenbury Wells, Worcs; but do mail order. Look at page 43 of their catalogue where they list a DIN plug and socket rated at 16A max. which will take your 12A rated compressor.
You will find fuse holders of all sorts in the catalogue, find one that takes the same sort of fuse that is already used in your vehicle, but don't overload the circuit or fit a bigger fuse than the rating of the socket. Cable is at the front, select some to suit, page 3 multicore cable - 2X28/0.30 is rated at 17.5 A so will take the 16A from the socket safely. 
Site the socket somewhere safe, connect it to a heavy circuit; suggest fridge size or larger; but disconnect the battery first and test all connections as you go to make sure that they are 'good', for which you will need a multi-meter, hence suggest auto electrician. But at least if you look at the catalogue on line you can see an indication of what is needed so that you can check that the bits instaled are exactly what you need, and not what they have at hand, which is possibly what has led to the big fuse in your extension lead.
Sorry if this is a bit long, but hope it is of some use.


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## jiwawa (Jun 22, 2007)

Thanks for that BJT - I think with my level of expertise I'm better calling in those who know! 

It's interesting that the compressor worked ok on its own from the socket but blew when the extension was in-line. Does something detect a huge-rated fuse (35a) and assume it can't cope? Would it do any good to go through all the fuses in all the boxes looking for a dud? I understand you to say it may have blown a fuse further up the line.

On the subject of fuses I'm only just remembering our first weekend away in the van, on the coldest weekend of last spring, the fuse for our water pump blew (5a). In my usual manner I replaced it but it blew again so I called a halt.

But our dealer had no compunction about replacing the 5a with a 7.5a and it's worked happily ever since. Do I need to worry about this?


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## pippin (Nov 15, 2007)

No, the 35A could not be detected by anything - electrical ccts are not that intelligent.

It is patently obvious to all of us with any electrical knowledge that the fault was caused simply by a short cct in the extension lead.

The presence of the 35A fuse simply transferred the failure to fuses of a lower capacity further towards the battery supply.

Your first step (other than calling in an expert) is to pull out fuses one by one and visually inspect each one.

Do it one by one and remember exactly which one came from exactly which socket - especially as not every fuse socket is populated.

Regarding the water pump.
It is not wise to replace a fuse with a higher value, as you found to your cost with that 35A one!

However even the experts can sometimes get it wrong!
An example is the humble domestic vacuum cleaner which suggests from its rating plate that it takes less than 5A and so has a 5A fuse in the plug top.
But the start-up surge is much, much higher than 5A but it is very short-lived and is within the short-term overload of a 5A fuse.
Unfortunately it stresses the 5A fuse and after a few start-ups it says sod-it and fails.
So, one substitutes the 5A fuse with a 13A and all is hunky dory as the cable is capable of handling that overload.

Unfortunately it seems that the UK has standardised on 3A, 5A and 13A fuse sizes but in fact they are available in 1A, 2A, 3A, 5A, 7A, 10A & 13A ratings.

I personally use the other ratings as appropriate as I have accounts with suppliers. 
You would be hard pushed to find the other values in most retail outlets, which is a shame.

This brings me back to the issue of your water pump fuse!

As it is an inductive (motor) load it has a higher start-up current than its running current.
I suspect the van designer looked only at the running current and your dealer upped it to the next higher value. I suspect that the cable can easily handle the possible extra current should there be a fault that takes the current up to 7.5A

Phew!


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## BJT (Oct 31, 2008)

The cab lights and alarm will be fed from a circuit that is permanently 'live'. i.e. fed from the battery. There will be a second fuse board with higher rated fuses giving primary protection to the final circuits.
Your vehicle manual may have a schedule of fuses indicating where various fuse boards are located, and which fuse protects what. Look for the one marked 'interior lights' or possibly 'cab auxiliaries'. Good hunting.


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## jiwawa (Jun 22, 2007)

I have 4 fuse boxes in the 2007 Transit:
1. Pre-fuse box
2. Standard Relay box
3. Passenger compartment box
4. Engine compartment junction box

There's a fuse in the Engine box rated 40a which protects the ignition feed to Passenger junction box - which is where the (still intact) fuse for the cigar lighter is. Would this be a good place to start?

Is there anything I need to do before checking this fuse? I guess I should switch off the 12v to the living area - anything else?

Thanks, I really appreciate the advice.


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## jiwawa (Jun 22, 2007)

Found it! It was in fact a fuse 2 along from the one that was billed as for the cigar lighter - one called auxiliary power I think (I've left the book outside). A 20a fuse, so I was lucky! The alarm and the cigar lighter are now working again. The internal cab light doesn't seem to be though, without the ignition on - but maybe it never did; I don't remember using it before.

Now to organise a proper extension lead.

Thanks for everyone's help and support.


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## BJT (Oct 31, 2008)

Well done, pleased to see my guess for the circuit identity was not far off the mark.
If the interior (cab) lights are not working when you open the cab doors check the switch on the cab light assembly. Some have three positions - you might try moving the switch to see if the lights come on in one of the other positions.

Regards,


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## pippin (Nov 15, 2007)

And remember that the light will go off automatically 60mins after the ignition is turned off. As will the radio.

There is a peculiarly-named fuse that controls it.


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