In all situations where there is a fault in electric equipment, identifying a wire (signal) from one point to another is a headache. Pulling the wire to see if it moves along the way may be not the best practice but in most cases the only way. Also checking the continuity or resistance may be dangerous if the wires are alive.

Any idea of a manufacturer of:

1.- An instrument that can measure Resistance over energized circuits (in places that is impossible to measure current)

2.- An instrument that can identify a signal cable from one point of a terminal block (TB) to another (TB). May be energized wires.

 

You can make some really good guesses with a voltmeter. If the ends show a low voltage there's a good chance that there is a wire between them. I know that's kinda weak, but..... A fox and hound can be made to work to some extent even on energized wires but you want to think carefully about what you are doing. And obviously it's not a good idea to inject signal into analog circuits. I've used a DSO before, if both points appear identical........

Regards
cww