Can you use speaker wire for 5x12vx20W halogen indoor lights?

Answer 1

That depends on the speaker wire.

Understand that the 5 halogen bulbs will result in about 8-1/3 Amps. That's pushing it for some speaker wire. The 12 volts falls in the category of low voltage wiring, so speaker wire insulation probably be okay.

But if it's normal, light duty speaker wire, it will probably overheat if you try to push that many amps through it.