1989 silverado 1500 stereo wiring?

The closest diagram I have found was 1989 silverado 3500, I thought it would be the same but the colors are all wrong.

This truck came with the factory radio which was a separate receiver which had these wires connected:
Red, orange, yellow, brown, white, and black.

and a cassette player which had these smaller gage wires:
brown, orange, gray, black, blue, blue w/ black stripe.

The only thing I have figured out is that the larger black is ground, red is ignition. I used a little bulb to test them, I don't have a meter. Using the bulb, none of the other wires had power, switch on or off. I used a battery to try and find the speakers, the only sound I got was with the blue with a stripe on negative and the gray or black on positive, other than that, nothing.
Anyone who has the schematics or any other info would be appreciated! Thanks.

There is a third piece of that system.  Follow the wires from either piece you see to the Tuner/Amplifier module.  You will need a 7 MM nutdriver or ratchet/socket setup to remove it.  There is one screw towards the firewall of the vehicle, and one at the other end of that same bracket, it is right under the dash just in front of where your right knee rests while driving.  It has been many years, there may be a third screw.  The wires you need are plugged into the top of the tuner/amp module.  There are 3 plugs there.  They are the colors you need.  But may I suggest going to a stereo shop and purchasing the 15 dollar harness.  If you do not get the harness you may have to extend every wire on those plugs to get them to reach where the new radio is to be mounted.