We've had a few blank wall plates around the house since we moved in a few years ago, wondering if I can patch over them to cover them up, or repurpose them. Seems like the first one is for a phone or a thermostat based on the height, but I don't know enough about wiring. Guessing the second is leftover from an old central vac system. Thanks for the help!
The first two definitely look like old telephone wiring. The black, red, yellow and green were definitely Bell system colors before they started using paired conductors. The higher up mounted box could have been for a wall mounted phone. The third box looks like, as you said, a whole house vacuum cleaner system. The wires shown went to two, low voltage bare contacts that closed when the metal part of the hose was inserted in the cover plate shorting out the contacts and turning on the vacuum motor that was usually mounted in a garage or utility room.
You could patch over them but by the time you did that, matched the texture, repainted the area or entire wall, they would still be more noticeable that if you just left the cover plates on.
If it isn't phone, the first box could be alarm system wiring, which also is commonly installed with the same cable.
My current house has this wiring, installed into similar covered junction boxes. It's obviously not phone because while there are some mounted at arm height by entrance doors, other boxes are installed on ceilings and high on walls.
