Stereo replacement - ISA harness adapter question.

I'm sure this question has been asked before but I'm replacing the original stereo from my lad's 2001 Micra with a new Pioneer unit. After a little trial and error I appear to have got the correct ISA harness adapter from Halfords even though it's supposed to be for earlier models ( but I can see that there's a long black wire with a metal eye at the end included in this adapter - presume this is an earth wire but do I actually need to connect it to something as I'm sure I've read on here that Micras earth through the arial?

Thanks in advance for any assistance.