Best way to do it,B&Q it!

[Joloke]

DIY  DIY DIY

[Uncle Jimmy]

Short of using battery leads I don't think it can be too thick? Regular wiring will be too small to cope with the amperage I guess- could be dangerous too. I'd veer on the thick side, can't see higher resistance being much of a problem.

[sierraman]

I'd make a trip down the breakers and cut a length of cable from the starter feed. Should be right gauge of wire, cost will be a few quid.

[Asimo]

I would clean the wires where they pass into the connector and in the junction box so the colours show and then photograph the thing at each end so you you have a reference to rebuild from.  Put the photo up here.

 

Then remove the cable assembly complete. Photo again.

Replace each wire with similar wires - same or larger cross section of copper. Don't use wire with a small number of thick strands because it won't cope with engine vibration and will break in no time. Make the assembly a bit longer than before, no tight wires when installed this time.

 

Don't try and use wire that is too thick for the terminals - that always leads to trouble!  Loom the wires together with PVC loom tape in approximately the shape the assembly will be in when it is installed. Knot the tape at each end so it doesn't unravel when it gets hot

 

Two alternator output wires of the same thickness are probably just used because two wires of half the cross section are more flexible and are easier and cheaper to terminate than one thick wire.

 

Good luck.

[Jifflemon]

Photo's definitely help, but my tutor taught us many, many years ago, "if it'll carry more, it'll carry less".

 

If it's a standard 3 Pin Europlug, we use to use two lots of 27amp cable (one per pin). This sort of stuff (*NOT* endorsing buying from halfords, just the first link I clicked)

 

http://www.halfords.com/workshop-tools/garage-equipment/fuses-electricals-fixings/halfords-27-amp-cable-red-hef741