Electrical fire sparks electrical question

[Doc007]

My 2016 Duratec had a "slight" issue when it tried to set itself a flame. I went to start the engine with a weak battery when smoke started pouring forth through the cigarette lighter socket. Fortunately, the fire died down and I was left with relatively limited damage to the loom near the fuse box. My car is being assessed by a garage but unfortunately my insurance company has walked away as they say there was no fire (despite light/ash/smoke/burnt wires). 
Anywho, my question is this; there has obviously been a short for some reason and it looks like replacing the loom is a distinct possibility. Obviously this is a potentially HUGE job and I'm seeing if corners can be cut. Could a problem with the wiring distant to the scuttle cause a short under the dash on the passenger side? If not, then cutting and joining the new loom onto the existing front light/rear light wiring could save a lot of time any money chasing and replacing them.

Oh and anyone got a good recommendation for a small fire extinguisher? It's made me a little paranoid... 

[SM25T]

It's a good reminder for everything to be fused with an appropriate rating.

[Jonathan Kay]

Sorry to see that.

I don't know.

Do you have all of the wiring diagrams that you need? I have a large collection including some that never appeared in Assembly Guides.

Jonathan

[OldAndrewE]

That was not necessarily a short.  It could be that a wire ended up carrying far more current than it was meant to and overheated, melting the insulation.  As SM25T said check that all your fuses are the correct rating

[Jonathan Kay]

"It could be that a wire ended up carrying far more current than it was meant to and overheated, melting the insulation."

And with it happening on trying to start the engine in addition to the wiring that includes the starter switch, the relay, the solenoid and the starter motor.

Jonathan

[Benton]

That was not necessarily a short.  It could be that a wire ended up carrying far more current than it was meant to and overheated, melting the insulation. 

 

Agreed a very possible scenario, the other cause could have been  pre-existing physical damage to the wiring at that position  but then something would have needed to disturb it at the time of starting to physically create the short.

Looking at the pictures I'm guessing it's almost impossible to identify what wire started the whole thing off?

 

I'm no electrical engineer and I could be talking total utter tosh, in which case I apologise  in advance! but ..... is it possible (at least in theory) the  "intended" earth path for one of the more current hungry components involved in start up for some reason wasn't available and instead found an alternative earth path through less current capacity wiring, that in this scenario bypassed any fuses?  

[Hampshire West AR]

Not sure how much work you normally do on your Caterham but if I was doing it myself I would remove the scuttle and remove the loom tape to identify the melted insulation, and using a wiring diagram ascertain what circuits are affected.  If the damage is limited it may be possible to repair the loom.  It may be difficult to identify the cause as it could be a number of different things.

[rj]

And it could also be caused by a poor earth, especially when it happens during cranking

 

[Doc007]

Thanks for the offer Jonathan, but electrics are a foreign language to me. Leaving it to the pros.

 

[Doc007]

Thanks chaps.

And as for my question about whether it is possible that a short/other electrical problem at a site at the front or rear of the car being able to cause the problem under the dash?

[revilla]

Yes it is possible. For example a short in the rear lighting units could lead to a high current traveling down the wires that run all the way from the fuse box to the rear lighting are.

This is why it is important to try to identify the root cause; you don't want a replacement loom or loom section to go the same way.

I would expect these circuits to be mostly protected by fuses, although something clearly wasn't here.

[ChrisC]

I commented on these photos when they where posted on Facebook, recommending a replacement chassis loom, and a good inspection of the dash, switch and engine looms.  Given it looks like the solid brown wires are the wires that have over heated, the brown wires are the pre fuse power supply wires to everything electrical in the car (except the starter and alternator) so you have to expect anything could have been the cause.  If it is the solid brown wire that has overheated incorrect fuses won't be the problem.  That said, I noticed you seem to have a mix selection fuses from different brands, technically not a problem but it might mean the cars has had previous electrical problems.  Do you know the cars full history?

If it was my car, a replacement chassis loom would be they way I would go.  If that wasn't an option, I would still want the loom out, stripped the wires replaced and reassembled to gain piece of mind.  Those brown wires have a few joins where they split into multiple wires, it's highly likely your only seeing the obvious damage and there is more to be uncovered.