You can use a littlefuse miniblade add a circuit and tap the lighter socket circuit in the fuse panel on the passenger side dash that goes on/off with ignition. That way the installation is completely reversible w/o hacking factory wires and also separately fused.
1st- get a hardwire kit for the specific R.D, and wire it into the fuse box with a acc fuse.
2nd- the way I did it to my valentine, I lost my hardwire kit it came with. I had a old 12 volt socket deal laying around so I put a + and - to it and wired it to the fuse box and plugged my R.d into it and bam hard wired ha..