Wiring diagrams for base and "deluxe" sound systems:
You must be registered for see images attach
You must be registered for see images attach
Other than the speaker feeds you are dealing with only 3 wires on the original side of the head unit to chassis wiring connector.
The Chevy yellow wire - main power. It is switched on when the key is in either the run or accessory position. It should go to the red wire on the radio.
The Chevy gray wire - lighting supply. It should go to the orange/white wire on the radio
The Chevy black wire - ground. It should go to the radio's black wire.
If you are having problems when the parking or headlights are turned on, there is probably a short in the illumination wiring circuit (gray- to -orange white). It plugs into the fuse block at one of the "L" sockets. Pull the gray wire from the fuse block and see if it resolves the issue.
Orange/white is the aftermarket standard color for head unit lighting - but without a make/model of the head unit I can't say for sure.