My Seven is working again, dammit!

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Out in the Seven the other day and it stopped with an interesting electrical fault. No ignition, no lights, no indicators, hazard flashers, windscreen wipers etc, absolutely nothing, dead as the proverbial door nail.
On getting the car back home checked the battery and chassis earth connections first as these can often be a problem on this type of car, and these were all fine, With the battery showing 12.9 volts the car was still as dead as a door nail.
Did a check of all the electrical connections including all the fuses, and modules in the fuse box, and could not find an obvious fault. I left the car for a while whilst I consulted the various manuals I have for the car, and on returning to it, (as I remembered I had not checked the fog light switch), the damn thing was working again, and fired up at the first turn of the ignition key. which p*ssed me off big time.
When a fault is found and suitably corrected, that is OK as it is possible to trust a car`s reliability (to a normal extent thereafter) but when a car just stops completely, and then starts running normally again for what seems like no apparent reason, it is difficult to trust its reliability. Any one else had a similar experience where even the headlights, and hazard flashers stopped working even when the battery had a good charge in it? Any suggestions would be very welcome.

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Krikkit said:

What kind of fuse system is there? It almost sounds like a giant fusible link which has then reset itself after a while... I'd keep a multimeter in the car with me so if it happens again you can be straight on with checking how far the live gets you, and whether you've got continuity to the grounds etc.

Thanks for the reply. The first thing I checked after getting the car home was the power in the battery (not least because the car was completely dead, without even lights or hazard flashers which should in theory keep working even if the engine wont run), and the earth connections, (where I took apart and re made all these), to make sure there was not an earthing issue, as these can often be a problem for seven type cars, but the car remained completely dead with no apparent electrical power whatsoever in the car despite the battery being at 12.9 volts, not even for the side lights.
There is no large fusible link in the electrical system it is not that sophisticated a system.
What is so frustrating is that the car just stopped all by itself, and then for no apparent reason, (certainly nothing that I did) started working again all by itself.
I really wanted to pin down what had happened so that I could correct it myself, or at least I would be able to understand what caused the problem if it happens again, but now I have a car which is working normally again, but I don't have a clue as to why it packed up, nor why it is working normally again..

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RicksAlfas said:

I would really check all the battery lead clamps. I had a crack in one once which was very hard to spot. It usually worked but every so often would leave me completely stranded. I'd wiggle everything and it would work again...

Again thank you for your reply. I re made all the earth and battery connections including filing the battery terminals to clean lead before re connecting them, and covering the terminals in Vaseline, but the car was still completely dead, despite having 12.9 volts in the battery. It is not knowing why (absolutely everything including the lights and flashers) it stopped, and worse still, why it started again all by itself, which is the pain in the backside.

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The Ors said:

Sounds like something got hot & then cooled down again.

What kind of time between stopping & then working again? You may have to drive round & round the block until it stops & then investigate.

I had the temperature thing doing this on a Spitfire I had many, many years ago, which would run normally when it was cold, but would stop when it got warmed up. It turned out to be a broken low tension wire, where it would transmit electricity when cold, but as the engine heated up, the plastic sheathing would expand pulling the two ends of the low tension wire apart. When it cooled down the sheathing contracted putting the two ends of the wire back in contact with eachother, after which the engine would start and run until it got warm under the bonnet again at which point it would stop again. I could not work out what was happening, and it baffled the auto electrician for half a day before he discovered what was going on.
In the case of the Seven I had just taken it out of a cool garage and only run a couple of hundred yards up the road, so it had not even started to warm up under the bonnet when it conked out. I checked the major circuits with the multi meter, and they all seemed Ok but the heat aspect could still be a possible culprit. Rather than run around the block, I will run the car on the drive, until it gets fully warmed up, and see if it keeps running, once the engine, under bonnet wiring, and surrounding bodywork and structure have all been heated up by the engine. Again, thanks for you reply