Finding out what cables do or what they are connected to is not complicated at all, it also involves no special equipment.
A multi meter can tell you if what they are connected to is live or dead, it can not tell you the route of a cable.
There is such a thing as a "voltage stick" but all that does is tell you if a cable is live or dead by bringing it into proximity of a cable, trouble is they do not work on extra low voltage and most do not work on D.C. current, and if they did, as they work by being in proximity you would only need one cable in a bunch to be live to indicate that all cables are live. You can get "cable tracers" but the good ones are very expensive and you still need to follow the cable.
Conclusion If you want to know if a cable is no longer used, follow it from one end to the other and check what it is connected to, it's cheap, and it works.
My problem is that not only are the wires bundled and painted together, but disappear into false ceilings or into walls, so I cant really follow them end-to-end, which is why I was hoping there was another way of figuring things out.
I guess I might just have to find a better way of concealing them!
I have to admit they do not look particularly nice, but I have a further suggestion. (It is what I would do) The wires are like they are as they have been added to over time with each person following the original cable route as required. Often when this is done the cables will be pulled tight and have no slack (So you can't move them) I would install new cables using a different route, even if that means taking up floorboards (Which I would guess is the reason the cables you have are where they are, as the previous person just took the easy option.) Then you can remove all the old cables. Yes you will still have to follow the cables, yes it will take time, yes there will need to be some making good, but it will be worth it. I would start with the easy ones. (The ones you can easily follow)
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