The red positive cable to my father in laws Fiat panda (56 plate) sheared off today at the terminal. It looks like its been worn by vibrations over the years and finally gone. I replaced the attachment to the battery but even though 12v across battery the starter isnt going. The radio, lights and central locking all still work for now. Checked all the fuses and no breaks.

Could it be a relay somewhere ? Is this a common fault ?

Cheers for the help
GG

I assume you mean the terminal at the battery. These cables, and the earth cable, are prone to corroding inside the sheathing, so can have breaks along their length. If the top connection has a break, you also need to check for continuity along it, and especially the terminal at the starter. If you have jump leads, connect one end to the starter and the other to the battery, (connect at the starter first, but keep it away from any earth point.) If it then works ok, you'll need a new cable.