[1letterunixname]

The higher the voltage, the less conductor but more insulator are needed.

Said another way: the conductor is rated for amps and doesn't care about volts, while the insulation is in volts.

In an urban environment, there are many opportunities to salvage. Industrial areas especially have good pickings.

Rural environments are limited by the lack of salvage opportunities.

Don't bother trying to salvage wire from vehicles for anything substantial. Find the lowest effort option to improvise based on what's available.