Colin Utting

Have just bought a 1993 LS400 and fitted a car phone kit (Nokia CARK91). The kit has a wire that is 12volts normally and drops to 0volts when the phone is in use. I know I could buy a relay to switch the speakers, but does anybody know if there is a connection on the radio for muting it. I have a wiring diagram for the audio system, but the wires are just labelled with codes and I do not have the key to work out what they are.