What do black dots represent in a wiring schematic?

Answer 1

A black dot in a wiring schematic diagram at a wire intersection represents a position where circuit wires are joined together. At a wire intersection where there is no black dot the wires cross over each other with no junction.

Answer 2

Black dots in a wiring schematic usually represent a connection point where individual wires come together or join. It signifies where two or more wires are connected in the circuit.