Good Morning Chaps,
Chasing the correct amperage of the brown wire from the ignition switch to the solenoid?
Thanks

High enough to not let the smoke come out ?

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1970 Mk2 Cooper S under restoration

If you are talking about the wire itself then BMC specified them in number of strands. The brown wire is 44 strands.





If you mean the amperage of the circuit then the fuse box only has two fuses of 35 amps each that protect all circuits.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

3 or 4 mm cable will be more than big enough.

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Cheers Dave.

Its quite small at I think 1 to 1.5mm sq, so I might consider it about 15 amps continuous. Its the contact in the ignition switch which really drop the voltage though, they were never meant to work for 60 years or carry much current other than the ignition load.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Already posted a reply that doesn't seem to have got through.....

The alternator/ generator wire winabbey mentions is 44 strands of 0.012 (0.3mm) wire and rated at 22 amps by the factory. 22 amps was the max output of the generator and about the same as the first alternators.
Like Steam said, 3mm sq. is is 44 strands/ 0.3mm and rated at 33 amps;
4mm sq. is 56 strands/ o.3mm rated at 39amps. Either should be enough for basic loads.

If you have a higher output alternator, you will need a suitable amp wire and possibly larger terminals like modern cars.
The solenoid to alternator wire doesn't go through the fuse box so there is no 'safety' factor from the fuses.
As Mick says, a lot of things ran directly off switches that were just able to cope with expected loads but not intended to handle extras, like driving lights running directly through the panel light switch.

Thanks Bill, I was of the impression the wire to the ignition was a smaller diameter, but it must be the same size as in the BMC technical file Doug put up. Ta.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I have mixed up the generator to solenoid wire with what you're after - the solenoid to ignition switch. Ignore my comments about alternator outputs.
Still remains what winabbey said: 44 strands/0.012" (0.30mm) at 22 amps on original wiring and with modern wires 33amps - called 3mm sq wire.

Also beware of the different cable sizing systems. Automotive wire is measured by its diameter whereas all other cables are measured by Cross Sectional Area (CSA or Square)
A 4mm auto cable has a CSA of 1.84mmsq whereas a 4mm CSA has a diameter of Approx 6mm.

I actually measured the diameter of the wire yesterday afternoon and it is 2mm dia wire.

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Cheers Dave.

You have confirmed the issue I'm trying to get my head around: 2 different ways of measuring the wire - both in mm but sometimes the 'squared' is omitted.
Most of the wires I have been using are from UK as they have all the Lucas colour combinations. Their catalogue lists number of strands/diameter of each strand/cross-sectional area/continuous amps rating /O.D. of wire and insulation, so you have a chance of the right sized wire.

The small quantities of wire and connectors I have purchased came from local supplier JayDee. If you scroll down to the bottom of a page there is a catalogue section that includes wire specification.

https://jaydeeautocables.com.au/

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

And just to really confuse things the Yanks use awg.

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Cheers Dave.

AWG the same as B&S. They are identical. AWG (American Wire Gauge) and B&S (Brown & Sharp) are both American Standard Wire Gauge Standards.