I don't have the wiring color codes, but the Metra 70-1677-1 was the right harness for my '92 Cargo van.
Yes my local audio store was able to save me. But I looked around on the ol' interwebs here and found the codes so might be worth it if someone else needs them by chance.
1989-93 Chevrolet Van (fullsize) Stereo Wiring
Constant 12V+ Orange
Switched 12V+ Yellow
Ground Black
Illumination Gray
Dimmer Brown
Antenna Trigger Pink
Antenna Right Front
Front Speakers 4" x 6" Dash
Left Front (+) Tan
Left Front (-) Gray
Right Front (+) Light Green
Right Front (-) Dark Green
Rear Speakers 6" x 9" Rear Doors
Left Rear (+) Brown
Left Rear (-) Yellow
Right Rear (+) Dark Blue
Right Rear (-) Light Blue