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Fuse Keeps Blowing


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I have a 2001 S-Type 4.0 V8 and it has blown 2 fuses as soon as I changed them.  The fuse is no 7 in the drivers footwell.

It has knocked out the drivers electric seat controls, electric mirrors and it has a list of a few other things as well.  Having trouble with the key fob central locking as well the same time they stopped working.


Anyone got any idea what would cause this to blow?


Thanks, Brian

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Hi Brian -Welcome--It sounds as though you have a live feed going to earth somewhere .???

I think if it was me I would be checking the mirrors first to see if you have a wire off or

something like that .???



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hi Brian

if its putting the seat electrics out I would try disconnecting the seat wiring then replace the fuse if it still blows you will know the fault isn't the seat electrics you could then disconnect the next easiest item to get to that's feed buy that fuse until the fuse doesn't blow the last item you disconnected will be the one with the fault.

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Hi Brian,


Follow Chris's advice, this is standard diagnostic procedure that I was taught 30 years ago when a new engineer and it's served me well since then.


Of course it could be a fault in the loom which is a little trickier to fault find on but;


"Always check the easy stuff first"

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Brian, there are only two things that can cause a fus to blue being;

1. A direct short in circuit (Live to Earth[ground])

2. An overload in current.

Due to the fact that the fuse is blown immediately on replacement I would be 99.9% sure it would be a direct short. I would agree with Christopher's advice due to the fact its common practice to follow this route and it is also common for wiring going to seat movement devices to have become entangled in runners and the like which would be earthed therefore, live wire to runner earth = direct short

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All good diagnostic advice so far but don't be tempted to put a bigger fuse rating in as that will lead to the loom Melting . Look at places where cables flex such as door hinge areas as they weeken with age/ constant movement

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Hi Guys


Trying to get to all the seat controls to disconnect but looks a lot easier with the whole seat removed.  Having some difficulty with that because the seat is all the way back and cant get the plastic trims off to expose the bolts.


Any ideas or way I can progress?



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  • 3 months later...

Hello experts


Car has just come back from the garage and £173 lighter and still not fixed.


They disconnected all modules and still blowing the fuse as soon as it is put in.  They also think there is a short somewhere but could be a nightmare to find and very costly in labour charges.


Any ideas where to even start looking as I'm not keen on car electrics and don't really have a clue where to start.  Do S-Types have a known area of electrical problems?


Cheers, Brian

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Fuse 7 is said to supply :-



Driver's Door Module (DDM),
Driver's Seat Module (DSM), Powertrain Control Module (PCM), Passive
Anti-Theft System (PATS) LED, security horn, power mirror.


That being the case and IF the garage did remove all the above mentioned modules then it has to be a short circuit in the loom somewhere.


I'd not describe it as a nightmare to find, because electrical wiring is nothing if not logical. The problem is that there is so much to check.


Armed with a decent DVM set to con-check, and the appropriate wiring diagrams, it will be a case of methodically working through from the fuse itself, probing further and further down the loom until the DVM indicates an open circuit, telling you that you have just gone past the problem.


This is a job that I'd prefer to do myself because it WILL cost an arm and a leg if you get it done at a garage, or even a competent auto electrician.


I've just had a good look at the diagrams for a car of your model year and I can see where I'd start from. I would like to know how they managed to disconnect the DSM though, with the seat screwed in place.


Not much I can offer in terms of encouragement Brian other than offering to send you the appropriate wiring manual (if you don't already have it) Unfortunately, you are a bit too far away for me to get involved "hands on".


As an aside, I have to say that I'd like to know why it cost £173 to disconnect a few modules though.


If you eventually do decide to get professional help, please find a good auto electrician though. Most garage mechanics haven't got much idea when it comes to electrics, whereas auto electricians do this sort of thing day in and day out.


As a forlorn hope, I assume this hasn't always been the case. Did you fit anything electrical or carry out some other maintenance just before the problem occurred which could lead you quickly to the local area?

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Thanks for your feedback and if you have some wiring diagrams that would be great.


Is a DVM some sort of volt meter?  Have a sealy basic thing but only really use it to check battery voltage.  Wouldn't mind have a go myself but think its a bit technical for my brain to cope with.


It's a pity because the car has just less than 40k on the clock but I might just end up selling it if I can't get it sorted and take a big hit on it.


As for the cost, 1hr standard charge for plugging it in at £90 and another 1.5hrs taking off bits of trim etc.  They say they spent a lot more time trying to find the problem but who knows!


What area of wiring would you go to first, do you know if the wiring in a particular place gets a lot of movement?


Car was ok when I first got it, I did a service, Oil, filter, plugs etc.  Also removed the wiper linkage/motor as it seized but didn't notice a problem until after, I think. It was a few months ago now.



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DVM is Digital Volt Meter Brian. DMM is, perhaps what I should have said but many years familiarity breeds, if not contempt, then lack of precision DMM is Digital Multi Meter and as teh name implies, can be used for different measurements.

In brief, if your meter has a resistance or continuity check function it will be ok for what you need. Usuallu there is a selection on the meter where, if you touch the two probes together, you get an audio tone.

I'm not at home at this time but later, I'll arrange for you to receive the wiring diagrams and will try to give you an idea of the way I would tackle the job.

Meantime, please PM me your e-mail address so I can get the wiring diagrams document to you.

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Hi Brian --- I think you should check The secondary junction box it is located on the
bulkhead in the LH side of the cabin near the ‘A’
post. It acts as a splice header to avoid having
numerous splices in the harness.
There could be a wire off or corrosion of some sort best to have a look .??


Well worth a try all the best.???


I've been trying to get a diagram posted but up to now no luck .???





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Hi all and thanks for your replies, especially you two with the PM's and pdf files.


What you have given me is a great base to go by but I just don't have the time at the minute to do anything.  With work its well busy now and coming up to Christmas I'm in the parcel industry and it just doesn't let up until January.  I also have other projects on the go, most notably the garage extension that I need to finish before the cold and rain come (it started a bit this week) and I need to get the roof on and sealed/water tight.  I need space and somewhere dry if I'm going to be pulling wiring apart and its just not practical at the minute.


With this in mind I have decided to advertise the S Type on eBay to see what the interest is in it's current condition with a view to selling if it gets to the reserve.  If not, once the garage is done I might keep it under wraps until January and look into it then.  Thanks again for your help guys.


PS, If anyone is interested its on eBay, I'm in Cornwall.


Cheers again :)

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Hi Brian,

One trick I used (as a vehicle electrician in a past life) was to put a Bulb (21w indicator) in place of the fuse, and with extended wires hang it from the roof grab handle so as you then go round moving wires under the dash  / seats etc if you disconnect the short / find the problem the light goes out...

Best of luck whatever you do,


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  • 1 month later...

Hi guys, me again


Just one last problem.  Fuse is blown so I have no power to drivers window but it is currently open.  Can I somehow connect up a 12v battery to give it power so I can close it.  I have wiring diagrams with 4 different parts named BT2, DD4, CA85 & DT1.  Is one of these the supply plug?


Cheers, Brian

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Hi Brian = I can see the way your thinking here -But if you put a 12v battery to the feed to the window

and that is where your fault is shorting out and you havent a fuse between the feed something will get-- Hot-?????

so I think if I was you I would pull some wires off in other words disconect these things you think are blowing your

fuse until the light go's out as mike has explained ----Best of luck.



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Hi Brian,

As Frank points out if the short is inbetween where you connect the battery and the motor then it could catch fire...

So, one way would be to get to the motor wires in the door and connect to a battery as you suggest BUT put a fuse in the circuit - if you don't have an inline fuse about then a headlight Bulb will do the same thing - this will limit the current (60W headlight Bulb at 12v will give 5amps enough probably to drive the motor. 

The motor should have 3 wires (not had mine apart to see) one ground or earth and 2 supply (up and down).

hope this helps,


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Assuming your car has 2002 spec wiring Brian, I'm hoping you have made a typo and where you have put DD4, you meant to put DT4.


This being the case, it appears that with 12v applied to DT4-7, earthing DT4-3 or DT4-4, will raise and lower the window.


If your wiring is 2001 specification, then it is still connector DT4. DT4-1 and DT4-2 requiring 12v and earth to raise and lower respectively, reversing 12v and earth as required.


Hope that helps.

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