Yes, it grounded through the antenna, and/or the mounting bracket of the radio. (Kenwood 880s are not floating case. the metal case and bracket IS negative ground.) That's another reason NOT to fuse the negative power lead of a mobile radio. If that negative fuse blows, you might not ever know until you burn up the shield on your coaxial cable by pulling 20 Amps of DC across it. Also, I don't know where you learned the bit about "Connecting positive first as always" ...but that only applies to replacing the battery. It is totally backwards with regard to hooking up accessories in a negative ground automotive situation. After everything is mounted and grounded, then and only then should you hook up the positive "Hot" wire,, and install its fuse LAST.