peanut;
In any series circuit, there can be 2, 3, 4 or even 10 individual devices. Each device will have its own different resistance, and thus each device will have a different voltage drop. Lets say there are 6 devices, a fuse, ignition switch, another fuse,a kill switch, an ignition coil,
and a Pamco transistor. When there is current flowing through all of them, each one will have a voltage drop, and that voltage drop is easily measured by placing your VOM test probes on each side of that specific device.
https://www.swtc.edu/Ag_Power/electrical/lecture/series_circuits.htm