As an automotive technician I run into certain signal or command circuits that read zero volts when troubleshooting. Some circuits will get shut down when a fault is detected. I want to know if the circuit is at least connected without having to get to the other end of it. (I'll worry about the integrity of the circuit after this test)
I often test ohms to ground and see the meter auto range around or read some high ohms on these computer circuits. Not always but mostly. OL has me looking at the harness closely. Some kind of ohm reading makes me look at pin fit on the connector before going any further.
Now to my example and question. I once had an ignition coil driver circuit that read zero volts. Next step was to see of it had any connection to ground through the computer circuit board. I did this same method and had OL. The meter topped out at 40 MOhm. Reversed the leads and switched to voltage now got -10v.
So why didn't the ohm meter register something when it clearly had at least some path to ground as indicated by the Reverse polarity voltage?
That circuit would normally show a square wave 5v pattern BTW