This situation occurred in a 1927-built multi-unit brick building. Now a condo type. The wiring is 2-wire with conduit - I think. Most of the duplex outlets are OK, but 3 or 4 in the Living Room / Foyer area show open ground.
I opened the faulty units and put in a new wire from the receptacle's grounding screw to the screw holding the receptacle to the metal electrical box. This did not correct the problem.
I don't think it would be possible to pull a third ground wire through the conduit buried in the walls - even if the two old wires were used to try and pull in 3 new wires. The old wires have the thick older style insulation and I have no way to determine the routing of the conduit in the walls or how the wiring is routed to different boxes in the circuit. Some of the receptacles on this circuit are showing correct wiring.
I can't see how I can connect grounding wires together when there aren't any. The ground has to be through the conduit itself, I think.
The building has hot water or steam radiators, so I am considering trying to use this as a grounding spot, where near an outlet, but I would have to confirm that they are actually grounded or could be made to serve as a ground. Would probably use a metal screw type hose fastener to hold the wire securely to the foot of the radiator. The radiator cover would hide the connector and wire partly. But I don't have a way to run a ground wire to some receptacles further away or on the otherside of a doorway, without having the wire being very visible running along the floor, over doorways and up to each receptacle.
Presumably this condition has existed for years or decades without any known adverse effects. Besides the potential for shock hazards, are TVs or electronics plugged in to these open ground receptacles at risk any more than when plugged into grounded receptacles?