Use the black wire in the wiring harness, and connect it to the black wire in the car's harness. This grounds the receiver. If you have a chassis ground (a braided cable) for the receiver, ground it to any metal screw in a metal frame piece under the dash.
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Use the black wire in the wiring harness, and connect it to the black wire in the car's harness. This grounds the receiver. If you have a chassis ground (a braided cable) for the receiver, ground it to any metal screw in a metal frame piece under the dash.