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Thread: Wiring short! How the f*ck to find it..

  1. #1
    Guest s13silvia's Avatar
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    Wiring short! How the f*ck to find it..

    Now I'm surprised at myself for having to ask this question, because I've made custom wiring looms and I've worked in and around various electrical systems for years as a tech - but this really silly thing has me a bit goosed.

    No point telling you the car, as it's the only one in the UK and it's closest relative has a completely different electrical system

    This also causes me problems when it comes to getting replacement parts but that's another story.

    So here's my issue:

    Battery, new and tested okay on another vehicle.
    Put onto this vehicle - also tested okay before connection.

    Start and idle car for 10 minutes, no problems.
    Blip the throttle (engaging the alternator) then smoke everywhere, from fuse box, from alternator and from the air-intake feed duct (f*ck knows where it was coming from). Lights dimmed (alternator fried) but engine kept running off battery.

    So today I get down and dirty with standard tests.
    Firstly I check my positive lead terminal - it has continuity with the chassis.. boo!
    I open the fuse boxes and remove the positive by-lead to test the thick positive-starter motor - no continuity (yay)
    I remove the out-put wire TO the alternator from the fusebox - continuity with chassis.
    I put the by-lead back on and remove every fuse in the box - continuity even with all fuses removed except for the 100A


    So how and where in the f*ck do I find where the short is coming from

    At present as soon as the negative terminal hits the negative post (with the pos. already in) I get big sparks and the alternator tries to go on fire.

    Annoyingly I can't just buy replacement alternators, and until I get to the root of the issue it would be a futile waste of money, so any help would be appreciated.
    Last edited by s13silvia; 25-11-2018 at 18:44.

  2. #2
    Bod for SXOC Memberships Jon's Avatar
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    I'm no expert on electrics, but the alternator does sound to be doing something unexpected.
    Could you disconnect the alternator connection to electrics completely, and then run your normal tests on the rest of the system ?

  3. #3
    Guest s13silvia's Avatar
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    Quote Originally Posted by Jon View Post
    I'm no expert on electrics, but the alternator does sound to be doing something unexpected.
    Could you disconnect the alternator connection to electrics completely, and then run your normal tests on the rest of the system ?
    I tried disconnecting it along with the b-post wire from the fuse box as it's also the obvious choice for a short-circuit given the plumes of smoke. But I'm still getting a ground of the live..

    This is what I get for buying such a rare obsolete car

    i'm acctually starting to doubt myself now that perhaps I should be getting continuity between the positive terminal and the chassis - I need to go check one of my other cars tomorrow now, this is going to drive me nuts

  4. #4
    Guest s13silvia's Avatar
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    Quote Originally Posted by Jon View Post
    I'm no expert on electrics, but the alternator does sound to be doing something unexpected.
    Could you disconnect the alternator connection to electrics completely, and then run your normal tests on the rest of the system ?
    Ahem - I retract my previous statement as I jumped the gun a bit, I d/c the b-post wire but forgot the switch connector on the rear- and hey presto the continuity has gone. Which is a major relief because it tells me no live wires have grounded. I can see one of the loom distribution plugs has melted a little, but hopefully not enough to cause damage.

    So thanks very much pal, fresh perspective / train of thought and it's got to the bottom of it

    So the short is inside the Alternator itself.. Grand indeed - however it leaves me with the concern as to WHY it shorted
    Last thing I want to do is get a rebuilt Alt for it to go pop, that's assuming the parts are indeed available

  5. #5
    Member ANDY black s13's Avatar
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    you don't have many options it seems,take it a part and see whats happened inside,might be a simple thing you can repair
    if you were going to get it repaired/rebuilt it makes no odds
    just digs in and fecks off
    UPDATE 26/04/15: Black '92 s13 (Still)awaiting new engine! Now doing full interior/loom strip,2015 still making things and aiming for less than 1000kgs,White '99 14a has the 23k engine from the blue 1 now fitted + lots of new bits (to be Mot'd then up for sale)2015 still not done,lost interest want to get the 13 done 1st,Blue '99 14a 23k sold as rolling shell 03/14,Green '99 14a gone now RIP jfc,2015 Was Daily driving my daughters 1.0 Yaris ,Now replaced with another yaris SR 1.3 for daily (fun) runabout
    "I think that in any racing engine,The nearer you are too it Disintegrating,
    In general the better its performance will be" Keith Duckworth Cosworth DFV and other Cool stuff

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    Guest mattvaughan180's Avatar
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    You might not have a short anymore it may have blown itself clear


    Sent from my iPhone using Tapatalk

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