What is the Chassis Ground wire for when installing car stereo?

[lanaflyhigh]

I'm replacing my factory Honda stereo deck with an aftermarket pioneer stereo (deh 4200ub). As such, I have bought a wire harness kit so that I wouldn't have to cut into my car wires. But while I've crimped the other wires together, I'm left very confused as to what to do with the black wire (grounding). It has a flat metal prong?/clip? at the end.

Do I just cut that metal part out and connect the pioneer's black wire with the wire harness's black wire as I did with the other wires??

or am I supposed to attach it to the black wire and fuse a 2nd line with that metal clip and attach it to a metal surface too?

I'm pretty confused. I tested the stereo out and it seems to work fine but the radio signal is terribly weak and quiet so I wonder if its because of the black wire?

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