There is a 2001 LS430 Electical Wiring Diagram (EWD) guide available from Lexus. It's the same for a 2003 and includes wiring schematics (not component schematics) + connector information. The Volume 2 Repair Manual also has a stereo wiring diagram in it.
The best after market hands free phone kit to use would be one that intercepts the speaker wires, not pre-amp wires or FM stereo/antenna wires. I'm going to be installing a Parrot CK3000 into my 02 LS430 because it can intercpet the speakers and is probably the most advanced hands free kit available.
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