Wiring Diagram 2002 Toyota Tundra

Assuming you're trying to install a head unit, first try this:

the plugs that go into the back of the factory radio, are in bundles of wires that run to another set of plugs just behind/next to them, back there behind the dash opening.  Unlike the plug(S) that goes into the back of your radio, these 2nd pair of plugs should plug right into a standard toyota wiring harness ( Metra 70-1761 or equivalent.).  From there, it's just a matter of matching up the wires of your aftermarket head unit's harness with the wires labeled on the metra harness.  for most aftermarket head unit's made in the last 5 or so years, the colors will be the same as the metra colors.

If all of that doesn't work, next you should try this harness from scosche.