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Fuses - UK vs USA


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1500 Spitfire


Failed my MOT today because horn and hazards not working.

Checked the fuse box and top fuse blown.

Popped in new 35amp fuse, reconnected battery and the fuse blew straight away.


Can't see and obvious wiring/earthing issues, but I'm no electrician.


After a google, I thought it might be the hazard switch or the horn stalk.


So the plan was, go buy several 35amp fuses and use trial and error to find the culprit.


Looked on Halfords web site and came across a review saying Halfords fuses are American spec and great care should be taken

when using them in british cars !!


Anyone come across this before ?










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I've not heard of this before and I am not saying that is the case - although not seen any evidence to support / dismiss. If unhappy about the US fuses, get another type from another motor factor.


By the sounds of it you have a significant shorting to earth, with sufficient amp to blow the fuse immediately. I have to declare that I'm not au fait with the exact 1500 wiring diagram.


A process of elimination will be a good starting point:


If it is either the HZ or the horn, I would isolate both units by removing the live feed to them.


Then pop in a new 35amp fuse and see what happens - if it does not blow, then one or the other is at fault.


Take your pick and replace the live feed to just one of the suspect units. If the fuse is okay and the item works correctly with the engine running then it's safe to say that unit (HZ or horn is okay) you will then be left with the potential suspect unit.


To confirm that, repeat the above process and see if the fuse blows - common sense dictates that should be the case.


If that is the case, then you will need to go through the wiring associated with that suspect unit; a workshop manual will be very useful so you can trace wiring route correctly + wire colour identification.


Hopefully you will find a dislodged wire touching earth as you investigate.


Just to confirm, try BOTH suspect units as described to ensure that you have the correct one; you never know both units may have electrical / wiring issues !!


Hope that helps ??





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horn is on the same feed as interior lamp,, i would start there 


as for usa spec fuses  ,  no idea 

this is the  review copy from the halfords 35amp glass fuses


so this seems to imply you need 17  not 35  ..how do you tell what spec they are 



copyI assume most people who buy this product are doing so because they have a classic car. Most British cars of the 50's, 60's & 70's used these fuses. The problem arises because the original Lucas product (part no. 188218) fuses are 35 amps and 17.5 continuous (the "holding" current). The original fuse will blow at 35 amps. The Halfords fuse uses the USA method and is rated at 35 amps and is continuous at 35, so it will not blow until it is well over that, probably 70A - which means it will do damage to your car.

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You could contact Stafford Vehicle Components or Holdens and they will despatch the correct items, putting your mind at rest.


I doubt very much you will cause a fire by checking through the wiring and substituting fuses as you carry out your checks.


The worse you may experience is a couple of sparks when you find the detached live wire brushing against an earthing point.


If you do not feel confident and some do not, then take the car to a garage who will be able to deal with the issue accordingly.





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so this seems to imply you need 17  not 35  ..how do you tell what spec they are 


I only use fuses that I know what the spec is.  E.g.:


or http://www.vehicle-wiring-products.eu/product.php/673/glass-cartridge-fuse-25mm


I can't remember how long the fuses we need are, but the listing makes it quite clear whether they are rated for continuous or fusing.  

I have always understood that the fuse rating for Triumph cars, where quoted, is the fusing current.



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