Assuming that your G8 has a Mullard/Philips AT1022 scan coil assembly it will be a simple matter to find out which tag the grey lead should be connected to. The line deflection coil unit consists of two symmetrical coil assemblies, L8109, L8110 and L8107, L8108. Pin 3 of socket K is the common connection to the coils and the separate sections go to pins 2 & 6 of that plug. Therefore it is a simple matter to connect the ohms meter to pins 2 and 6 in order to trace the common connection on the scan coils.
Some G8 sets made were fitted with scan coils supplied from other makers, certain sets made during the early seventies colour TV boom when there was shortages of parts. Nevertheless, it should be easy enough task to trace the unattached wire after referencing from pins 2 and 6 of plug K.