Ok, so here is my confusion, I run the 10A BEC on my elec 8th...and the negative wire has come off the wire to the battery.

HOWEVER, the BEC still works, still powers my servo when the esc itself is off and still has its green light. How can the BEC still have power when it now only has the +ve connected? I have removed the center esc wire as per the instructions too!?

It's grounded (negative) through the ESC battery and servo wire connections.

Make sure to solder the BEC power leads to the battery plug , will cog if you try to do different....