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 :wack:

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 :wack:

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.

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 ?

Quote:

---

Originally Posted by Jon

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.. :rolleyes:

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

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 :wack:

Quote:

---

Originally Posted by Jon

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 :thumbs::thumbs::thumbs:

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 :p

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

You might not have a short anymore it may have blown itself clear


Sent from my iPhone using Tapatalk