I have been looking at several different Lexus wiring diagrams and all of them have an "amp" wire that runs from the HU to the amp and it also runs to the power antenna relay. On the diagrams, it is simply labeled "amp."

What is going on with this connection? Can I disconnect it if I replace either the HU or the amp?

What exactly are you trying to do?

it is a 12v switched wire that controls the antenna and amp turn on circut. this circut is slightly different than an accessory circut in that it only comes on when the head unit is on, rather than the ignition.

lol. I don't know yet. Just trying to figure it all out. Thanks onelasttry!

I have an SC300 and ws woundering what color wire on the factory harnesses is the amp turn on wire. I have no sound and am pretty sure that is the reason why. By the way I am installing an aftermarket HU and would have to splice into that wire.

check out this site:
http://www.technicalhelp4u.com/

look under the heading TOP DOWNLOADS:
theres 3 files, one for tthe SC, one for the general pioneer, and one for the nak system. These are little demo things, and they will tell you what wires are what.

Where can I find the same info but for the stock stereo + CD changer of a 2000 GS300?

Thanks