Get your hands on a Digital Volt Meter. Set it to the DC Volt scale of 20 volts or so. Connect the black probe to a suitable ground location and turn the radio ON. Then, insert the red probe into the pins in the stock harness one at a time until you find one that reads 12 volts. Turn the radio OFF, if it goes dead that's your wire. You will want to then verify that the lead stays powered up on both the tuner and the CD player to be sure it wasn't designed to operate a power antenna when using the radio only.
It is possible that:
1. The stock deck doesn't have a turn-on output lead.
2. The stock deck does have a turn-on output lead, but it goes to 5 volts when the deck is ON and not 12 volts.
3. The stock deck does have a turn-on output lead but there is not a wire or pin in that spot in the harness in your vehicle since this wasn't required in stock form.
If # 1 is the case, you'll have to tie your amp remote to your accessory lead (the wire that reads 12 volts with the accessory or ignition ON and goes dead when the key is off.
If # 2 is the case, you can pick up a relay at Radio Shack that has a 5-volt coil. You can then wire one side of the coil of the relay to the turn-on output and the other side to ground, then the normally open contact to your 12 volt constant lead and the common contact to your amp turn on lead.
If # 3 is the case, you will need to locate a radio pigtail from a junk yard and pull one wire / pin out of it and then insert this into the OEM plug.
I hope this helps.
