old astras dodgy wiring question

[30psi]

Its not odd that it comes from the alternator if you think in reverse. In fact this is how I will wire up my car when I throw the battery in the boot.

The wire goes from the battery to the starter then from there on to the alternator. It just saves having 2 individual wires.

Whats worth looking at is what half the wire is melting. If it isn't the battery to starter half then that would suggest the starter isn't over stressing the wire.

If its the other half then it might simply be the condition of the wire as suggested or something off with the alternator output.

Would be an idea to check the battery voltage when its running at the battery, starter terminal and the alternator terminal to see if its consistent.