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Light switch melt


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Yesterday evening I took a short drive before dusk and had just the small side marker lights lit to begin with. The whole drive probably lasted 45 minutes, but probably 20 minutes in I turned on the dipped beams. Did not use full beam at any stage.

A little while later I noticed a hissing sound and quickly pulled into a pub car park to investigate. There was smoke coming out of the dash headlight light switch. I quickly yanked it out of the dash and the whole back of the switch was melted. The three terminals had fused together and pulled out of the back of the switch. The wires behind the switch were fused together and the lights stayed on. I partially separated them so the dipped beams went off but the side lamps stayed on and quickly drove home which took about 10 mins.

The brown and blue wires had melted together and obviously heat was travelling down them to the extent that about 2 feet of the brown and blue wires are melted/fused and partly stripped.

This is a brand new wiring loom from Autosparks equipped with relays for full and dipped beams and has only done 175 miles since restoration. The lights are Cibie units with H4 nightbreaker bulbs.

Apart from being completely gutted, I have no idea how this can happen. Do you think this is a fault in the loom, or was there a short in the switch? It is (was) the original clear hooters switch and there was a slight fault in the rocking action between off and position one for the marker lights in that it would struggle to stay in position one and want to either jump back to off or to position 2. Not sure if this is relevant as it seemed to work correctly in terms of turning on and off.

Anyone have any thoughts or suggestions?

Cheers,

Sean

 

 

 

 

 

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Hi Sean,

         I think your dicky switch may be the victim rather than the culprit.

If the internals had shorted out it would be the same as if the switch was in the full on position.

If you have the headlights going through relays then there would be almost no current to do that damage. 

You may need to follow the loom along its length to see if there is a short to chassis somewhere.

 

Roger

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If the short happened after switching low beams on, then there is a short following the blue wire. The blue wire goes thru the lever switch at the steering column. Maybe the cable is rubbing inside.

Jochem

Edited by JochemsTR
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1 minute ago, JochemsTR said:

If the short happened after switching low beams on, then there is a short following the blue wire. The blue wire goes thru the lever switch at the steering column. Maybe the cable is chamfing inside.

Jochem

Does the TR6 have the overly small cable cover under the steering column as per the TR4/4A. This is often a pinch point.

 

Roger

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Thanks Guys,

Jochems gets the prize. Looks like the snip that should cancel the indicator switch has been gnawing away at the blue wire. Not how this happened.  Unfortunately on closer inspection I've got blue melts appearing through the black loom cover deep under the dash. Looks like its dash back out time. 20190113_135538.thumb.jpg.86b44bff7c1153d7cab28fc98a901469.jpg

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You really do not need to remove the dash....going thru the main instrument holes should be sufficient.

Unwrap the cable loom to check the other cables, cutout the parts affected, get new ones and wrap them with the original loom again.

If you cutout and re-connect cables, try to solder them versus using connectors.

Jochem

 

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Wow methinks you were lucky!  Yes that cable cover is a good pinch point. When I had mine apart as it goes back together I keep pulling the wires back and forth to make sure they are free. Using modern cables helps a lot too. So get thin wall cable in the colours you require from somewhere like. http://www.vehicle-wiring-products.eu/ 

Thin wall cable has better abrasion resistance and can carry a higher load!

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Hello, couple of things, firstly, why not use 0.5mm thin wall cable instead of the 1mm, lighter and cheaper and the 0.5mm carries 11amp as opposed to the original 1mm carrying 8.75 amps, also the 1mm thin wall will carry as much as the 2mm standard cable.  I understand the reason is that the modern cable has much more efficient insulation.  Secondly, I think you were very lucky and your experience has forced me to fit an isolator on the earth side, I understand they were fitted to MGAs, a simple switch easily accessible from the driving position, it could save the car, cheers, Andrew  PS, I think you need to remove and check the loom, it could well be that you have damaged insulation somewhere.

Edited by AndrewMAshton
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Are the newly manufactured column stalks better insulated than the originals? How easy is it to rewire the originals stalks with modern wiring? I'm looking to avoid any melt downs before they could happen on my restoration- already have a full replacement modern wiring harness same supplier as SeanF so looking for best solution.

 

 

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Hi Michael,

I think the wires are soldered.

wish I had replaced them for modern wires with thinner insulation. And if relays are used, 0.5 mm2 should be more than enough.

also worth checking resistance of all the switches (use Ohm meter on the wires); resistance should be almost zero (say less than 0.5 Ohm. If more, use contact spray, that worked for me.

I installed the stalks for OD, light and flashers with the column on the workbench, that makes a better quality job possible. Think I held the long metal conduit with some ty-wraps during installation.

Waldi

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