The below comes from this site where you can get most any car radio wiring diagram for free:
http://www.modifiedlife.com

1997 Toyota T100 Car Stereo Wiring Diagram

Car Radio Battery Constant 12v+ Wire: Blue/Yellow
Car Radio Accessory Switched 12v+ Wire: Gray
Car Radio Ground Wire: Brown
Car Radio Illumination Wire: Green
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 5 1/4″
Car Audio Front Speakers Location: Doors
Left Front Speaker Positive Wire (+): Pink
Left Front Speaker Negative Wire (-): Purple
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Blue
Car Audio Rear Speakers Size: 5 1/4″
Car Audio Rear Speakers Location: Side Panels
Left Rear Speaker Positive Wire (+): Black
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Red
Right Rear Speaker Negative Wire (-): White

On EBAY, you can get a wiring adabtor that will fit the factor radio harness and have about 6" of labeled wires coming out. That way you can cut/splice these wires to your new radio and still be able to plug in and out of the factory harness. Cost is about $11 including shipping.

Hope this helps