I need to replace the cables that connect the battery to the alternator and the main earth cables from the battery to the engine/battery tray.

Two questions:
1 - It appears to be relatively straightforward - but whenever I say that something goes wrong so tips from anyone that's done it already are welcome.
2 - What guage/thickness cable do I need?

 

For the main alternator feed to battery something like 44/030 or 56/030 cable is normal, but some use 84/030 or even 97/030, personally I'd use 56/030 thinwall, this carries 39 amps continuous, about 70p/metre.
For battery to starter/earth I'd use 196/040 or 315/040, £4-£5/metre.
I just ran a 44/030 from the alt to the battery/power post on inner wing.
tabetha

 

The standard alternator to battery cable is 6mm^2, but if I was going to replace the equivalent on my saff, I'd use a bit bigger, say 8.5mm^2 (certainly if using a 90A alternator).

25mm^2 cable is suitable for the engine to battery earth.

The standard battery tray to battery earth is about 6mm^2, but if I was going to replace the equivalent on my saff, I'd use a bit bigger, say 8.5mm^2.

 

Good info guys

 

Thanks for the input

So something like this for the earth strap:
http://www.polevolt.co.uk/acatalog/info_PVC16B_110.html

and something like this for the alternator:
http://www.polevolt.co.uk/acatalog/info_PVC16R_110.html

would be OK?

 

The earth one needs to be much bigger, that shown is only 16m^, you really do need as I said 196/040, which is same as jon's 25mm^, carries 170 amps, as opposed to the one in your link carrying 110 amps, of course you could use much thinner for the smaller one to the battery tray area, here 84/030 would be more than ample!!, carrying 50 amps continuously, which you wouldn't use in a million years not continuously.
For the alt, if you want to REPLACE the wire use 84/030, ford did not use the same gauge wire for the whole run to the alternator, around 12"-18" into the loom it gets fed through a connection point, which is a sealed soldered joint, which corrodes terribly, and also goes from two wires into 1.
Although the alternator may be able to put out 90 amps(and most don't put out as advertised) it would die as a continuous load, my dads xr4i for example has a 34 amp alternator and manages fine, it's just nicer ford fitted a big powerful alt so it is not overworked, I'd be amazed if it was using over about 40-45 amps in use though.
Btw, www.vehicleproducts.co.uk is cheaper, and you may find polevolt have a minimum order, and that you need an account, so if you get stuck give me a shout, as I have one.
tabetha