How do you hook up factory 1989 silverado radio?

You hook the "high-input" wires from the amp to the factory speakers. This will serve as the 'RCA' cables.

there is an adaptor for those you can get from your local stereo shop cost about $100, it;s for the bose/onstar radios for chevy.

What you need to do depends on the vehicle you'll be working on, the LOC you choose, and the aftermarket equipment you wish to integrate. Pick an LOC and follow the instructions provided with it for...

U cant do it u dumb idot

there are ways to do this, but i dont recommend it. this can cause sound to be distorted and also could blow fuses or cause other electric damages.