['LIVEWIRE?']

The usual point in such circuits is at the point where the 8-pin socket is connected, i.e. between the preamplifier(s) and power amps. (TA7240 & 7241), so the connections should be cut at the points where the signals would pass through the socket. If radio & Cassette audio is still required then either a changeover switch or switched socket is needed, if not then the 'aux' input can be wired to the 'output' side of these points directly. (i.e.) the 'aux-in' signals should go to where pins 1 & 4 of the 8-pin socket are shown connected in the service manual, whilst the 'Radio-aux' changeover switch, if fitted, should be wired between pins 1 &3, and between pins 2 & 4. A screened lead should be used, with the screens taken to Audio ground-i.e. pin 2 on the cocket.