Being an old motor mechanic - found reading wiring diagrams in auto applications easier as there was a + & - and only used a test light (only started using multimeter since working on the pins) as well the wiring colours in the auto  stood out like dogs b....(cant rely on reading the colours in ems as they all look the same to me - Im a bit colour blind) - I feel more comfortable using continuity checking but I miss that main black earth wire.
This probably doesnt make sense as Im no electrician.Need to spend more time reading and working on schematics.