I'm getting a CB Radio soon and was wondering if I could hook up the ground wire into the existing wire nut connection between my JVC KD R530 and wire harness, or would that screw something up?
You can ground it on the same ground as your head unit, but don't use a wire nut. Those are for home wiring, not car wiring. You may find it easier to ground the CB radio to some metal under the dash. Make sure it actually connects to the body, which you can check with an Ohm meter.