how to find an open circuit between a cars battery and alternator?

Answer 1

The run from alternator to battery should be
pretty direct.
First 'run` the wire visually.
Then turn the engine off and check for voltage
from the battery to ground at each accessible point
to localize the 'open`or break in the circuit.

Answer 2

you would almost need an electrical print, because charge wire goes inside the car under the dash. that wire is hot all the time. so first thing i would do is check with volt meter or even a test light, see if there is power to the alternator. without knowing exactly what the issue is, don't how much more help i can be good luck