Fried wiring loom

[Hugh Dixon]

I have an issue with the lighting circuit on my spit 4. Fitted a new loom, lights etc but had smoke coming from the rear section of the loom a while back. I tracked it down to one of the new light units shorting out as the power feed bit was touching the bulb holder so a direct earth, clearly being a brand new unit this should not have happened. Fixed that and everything fine for months. Went for the mot yesterday and more smoke from under the dash board and the tester said there were sparks (?) coming from the main light switch ( which is an original unit) - not sure how it was visible when fitted to the dash board but still.

I have removed the light switch and the main wire into it has clearly got very hot, the wires coming out of it have also melted their insulation in a couple of areas. I suspect the rear light might have earthed out again however given the sparks, is the light switch defective as well or is this coincidental or as a result of the rear light shorting ?

I am not too up on auto electrics but wondered if the fact I have also fitted an alternator in place of the dynamo or the halogen headlights (the ones supplied by specialist triumph spares company) potentially contributory.  
 

has anyone else has issues like this ?
thanks Hugh 

[Hugh Dixon]

Mathew, yes I was thinking that might be part of the issue, am thinking to go back to sealed beam units , and of course they are more period. I didn’t look what wattage the halogen lights are before fitting and given they were from a main triumph parts sillier and didn’t come with any instructions regarding relays etc I assumed just a straight swap.  Thanks for response. 

[foshi]

might be worth a decent fuse box fitted , paul

[Pete Lewis]

the rocker light switches do fail and the arcing would only happen when switched on  the heat is easily generated within the switch contacts this moght melt the insulation near the switch itself not down deep into the harness 

in general halogen bulbs are same wattage as the old sealed beams  certainly not wildly different unless you fitted off road 140 watt bulbs  the norma lbeing 55/60 watts 

adding a supply via relays is quite easy and reduces the load in the dash switch and column  harnesses 

Pete

[Hugh Dixon]

Thank you guys. It’s a ‘63 spit so has the pull out switch but guess the same principle as the rocker one. If the same amp/ watt there should not be a problem but clearly y

there is more current going through given it melted the insulation. It didn’t blow the fuse (35 amp as per workshop manual) which I would have expected so I am a little stumped 

I am assuming if there was a direct earth then it would draw current sufficient to heat the wires but not enough to blow the fuse ?
 

I am a bit stumped given everything is new on the car other than the light switch but maybe that is the issue ?

[Clive]

14 hours ago, Hugh Dixon said:

Mathew, yes I was thinking that might be part of the issue, am thinking to go back to sealed beam units , and of course they are more period. I didn’t look what wattage the halogen lights are before fitting and given they were from a main triumph parts sillier and didn’t come with any instructions regarding relays etc I assumed just a straight swap.  Thanks for response. 

Most halogens, certainly bulbs supplied with lamps, are 55W, the same as sealed beams (give or take, but nothing to worry about)

However, relays are good as they take the load off the light switch, and can be beneficial in terms of light output. And that is the most important job of the lights!

The switch may well have been damaged by the earlier incident, from overheating and melting the plastic to burning contacts.

It can be very worthwile fitting additional fuses, protects the car against serious damage. 

[chrishawley]

It's perhaps worth thinking about the current pathways that might be related to this problem The dash light switch is fed via a brown wire from the starter solenoid. The red/green wire from the switch feeds forward to the fuse box and from there to side lights, number plate lights and instrument illumination lights. The blue from the switch feeds forward to the light switch on the steering column and thence to main or dip beams. Note that the headlamp circuit does not incorporate a fuse: Thus a dead short on 'red/green' would likely blow the relevant fuse quickly (assuming that short were at or after the fuse box). Whereas a short on 'blue' has nothing to stop it drawing down a heavy current.

Cooking the brown feed to the switch requires a hefty current. Changing from a sealed beam to a standard 60/55w halogen wouldn't cause a significant change in current draw. I can't see the alternator being implicated unless, exceptionally, it's gone over voltage. But that's easily excluded - voltmeter across the battery terminal with engine running; anything less than 14.5v ok (in this context).

For myself I'd place emphasis on getting a positive diagnosis of a significant problem, more than employing workarounds. An initial diagnostic might be as follows:

a) Remove headlamp bulbs. Disconnect dash light switch. Connect 'brown' to 'blue' through any suitable low wattage bulb (a front side light bulb will do for example). Switch between dip and main on the column switch. If (in either position) the bulb lights, however faintly, then a short is proved.

b) Similarly remove all bulbs off 'red/green' (a fiddle where instrument illumination lights are concerned - 4 off). Employ test bulb as before between brown and red/green. Again any illumination shows short circuit.

As mentioned in previous posts, a failing switch may arc, causing sparks, smoke and heat. Diagnosis is by substitution. But a test could be made by connecting borwn, blue and red/green together with a fly lead and then progressive reinstating all the bulbs, vigilently observing/feeling for overheating as one goes. If the circuits pass this test then diagnosis = switch.

Some other thoughts might be;

i) A hot spot for shorts in the headlamp circuit is where the wires run up the steering column to the switch. Can easily get nipped and create a partial or intermittent short.

ii) Does your vehicle still have a night dimming relay? The correct connections of this unit can be less than obvious. Or, if it's been removed/bypasssed then this has been done not leaving uninsultated terminals floating about.

iii) To check that main and dip beams are independent of each other and don't come on together. It is possible to get them connected in common which would impose greatly excessive current on the system.

 

 

[Hugh Dixon]

The fuse didn’t blow and I believe the headlights are around 50w so nothing that would draw too much power. I noticed it also melted the voltage stabiliser (a solid state one ) so assume there must be an issue in the loom now so will need to check that as well. So frustrating

so the consensus is to fit relays but I would not know where to start tbh - anyone have a wiring diagram or instructions where to take the feeds from plus relay types or is there something on line ? 
 

thanks for the help and advice, it’s so frustrating especially as I fitted a brand new loom to avoid this sort of problem 

 

[Hugh Dixon]

Chris, thank you for your response, that certainly gives me a number of things to look at. The car is a ‘63 mk1 so no dimming relay in the boot. 
think first as you suggest is to replace the switch - I see paddocks who I normally use stock them so will order one in. 
the gearbox is out at the moment which is a different story and issue so cannot run the car but in the mean time you have given me plenty of other bits to look at so thank you, really appreciate it. 

[chrishawley]

Ooops! I got it in my head that it was a Spitfire MkIV. Aplogies therefore that some some of the info will be off the mark.

[Pete Lewis]

in general melts are down to a distinct shorting rather than some overload , yes switches are aged and some canmake heat from poor internal connetions

but witha new harness fitted this seems more thats the problem either with the design of the harness or with the fitting and connecting there of

a carefull check of all thats been fitted is in order , 

how to pre guess whats wrong there are too mant things going pop to isolate any clues to help other than you need your sherlock hat on for a bit of research 

sorry not much help 

Pete

[Hugh Dixon]

Thanks Pete. It was a new auto sparks wiring loom. I am happy I wired up the loom as am familiar with the cars having owned quite a number over the years. 
I know the original smoke months ago was the rear off side light unit which was shorting out as didn’t have any more problems for 6 months until now. I think I need to look at various bits - steering column wiring, light switch, check the loom out I guess and I might put it back to dynamo just to make sure I didn’t wire the alternator wrongly. 
so annoying as have spent 3 years totally restoring the car and fallen at the last hurdle !

I feel a new loom may be needed and require the car yet again from scratch. 
thanks for the help and advice. 

[Paul H]

When I bought my Vitesse my electrics knowledge was minimal and set about testing each circuit adding relays where I thought they were required . I’ve also added an additional bladed fuse box . 
The best thing I did was to add an isolating link . This apart from extra security ensured I didn’t melt anything . I added a bladed fuse link with a 15amp fuse so removing the isolating bolt means this blows before any damage is done . I did go through a few fuses ! but no damage . The knowledgeable on this forum will help and advise whenever you need assistance . The siting of relays  is personal choice . See my location and it was relatively straight forward by breaking into the wiring loom and re taping afterwards .

Good luck 

Paul 

 

[AidanT]

Hi

 

Can anyone advise on the best place / position for halogen light relays in a GT6 please?

 

Thanks

[SpitFire6]

23 hours ago, AidanT said:

Hi

 

Can anyone advise on the best place / position for halogen light relays in a GT6 please?

 

Thanks

Near the Alternator or lights.
Fused off the alternator to protect that cable only to the relay(s). If they are halogen you will have the brightest light and shortest life of the lamps.

[dougbgt6]

I put the relays in the front lip of the bonnet, there are hand metal bendy bit put there to hold the loom.

Doug