old astras dodgy wiring question

[bigtim]

Mums astra has a main red power cable coming from the alternator to the solenoid on the starter then on to the battery positive but this short piece of wire from alt to starter is getting really hot and gradually melting its coating. Ive tested voltage at the bat and it seems normal(13.5) cleaned up the bat terminals and both ends of the red wire but its still getting warm.
Anyone have any more ideas.