It can be quite difficult to visually find an open circuit, since an oxidized or poor connection of contacts is often difficult to notice. Sometimes just moving a connection wire or a wire in a wiring harness is enough to fix this problem.
Unreliable operation of electrical equipment elements is also often caused by oxidized or poor connections.
Finding a fault in the electrical system seems to be a fairly simple operation, if you understand that the operation of the electrical system is based on the fact that the current flows from the battery through wires, switches, relays, fuses and burnable jumpers to the electrical equipment (light bulb, motor, etc.) and on (mass) car, from where it is fed back to the battery.
Any malfunction in the electrical system is an interference with the flow of current from or to the battery.