I was doing some rewiring behind the dash and accidentally shorted the main live feed - thick brown wire - to the ignition switch body causing a small zap and a spark. After that there was no power coming from the brown wire either connected to the switch or off of it. My continuity bulb didn't light and the multimeter read 0V. Went for a cuppa and think, came back and the wire was live again and read 12.6V.

Anybody have a clue what went on there?

Now an intelligent person learns from their error but I continued working and shorted it again! and the same thing happened - no power from the brown wire. This time I waited and a few minutes later the power returned! Anybody have a clue what went on there?

AFAIK the big brown wire comes from the alternator/battery. Did the short cause a relay to stick or something else?

Went for a drive of about 20 miles and the voltmeter was on 14V at first then down to 13.7 at the end and engine off read 12.6V, which was where it was initially on start up.

I'm concerned that it may have cause some damage to the alternator or battery.

TIA

First, what car and engine do you have ?

miktdish said:

First, what car and engine do you have ?

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Cheers @miktdish It's an '85 90 with a 3.5 V8 Efi 14CUX.

All working fine now, just wondered what I did and why the temporary no power event.

I'm assuming that shorting the ignition switch power lead from the battery/alternator connection to the starter solenoid messed with the alt components or the starter relay? e.g. demagnetising/magnetising them for a while so no power? As working fine now I'm hoping no damage caused.

It was suggested that a poor connection or break might have overheated and lost contact when I shorted it and reconnected when cooled down. I've checked the connections and wiring to the alt, starter and all tight and good condition visibly.
Puzzling, I'll keep an eye on it.

I don't suppose it was a coincidence that you chose where to earth your bulb and meter was a bit dodgy itself? If not I'd go with the heating up a bad connection because I don't think there's a fuse protection on your car. It might be worth taking apart the connections and having a look before you find it refusing to start.

In the meantime though.

It is puzzling ... Is there no fuse on the brown wire ?
You can get thermal/resseting fuses ... perhaps someone has fitted one at some time ?

miktdish said:

It is puzzling ... Is there no fuse on the brown wire ?
You can get thermal/resseting fuses ... perhaps someone has fitted one at some time ?

CIRCUIT BREAKER STANDARD ATO/ATC BLADE FUSE TYPE (AUTO reset) Range from 5A - 30Amp

Blade fuse style circuit breakers suitable for the protection of electrical systems on all types of vehicles. Bulk deals available for 10, 100, 500

www.altecautomotive.co.uk

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Can't find a fuse for the brown wire.
If it is a thermal fuse I've no idea where it is.

boguing said:

I don't suppose it was a coincidence that you chose where to earth your bulb and meter was a bit dodgy itself?

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No, I used the same earthing point for both bulb and meter and it worked fine when live. I did think that and whether the bulb had blown but the meter confirmed no power.

Working ok this am so fingers crossed.

cappers said:

Can't find a fuse for the brown wire.
If it is a thermal fuse I've no idea where it is.
<snip> Working ok this am so fingers crossed.

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Don't cross fingers, disconnect/isolate the earth lead from the battery ...

And when you 'recconnect' use a wire with an inline fuse ...
And fit a main fuse (in the brown wire .
One of these would be a good idea, somewhere accesible, under the bonnet on the bulkhead for example.