Re: 70 Chevelle SS radio questions.
The new radio should have come with a connector on the radio itself for the wires coming out of the radio. There should have been another connector supplied that would plug into that connector with short wires attached to it that will splice into power, ground, lights, speaker locations, etc. When those two connectors are connected together the corresponding wire colors should be the same. You can now use the instructions to tell you what color wire hooks into where. You could just leave the old harness and run all new wiring between the connector and everything it connects to.
71 Malibu, Cottonwood Green, 396 BBC, AutoGear M22W 4 speed, 12 bolt 3:55 posi.