The bits I think I forgot to mention.
The terminals on the relay (85,86,87,30) will be stamped on the bottom on the relay next to the legs (terminals).
Relays can handle lots of current. So don't mess around with the wire you use. Gadget will probably tell you the actual size needed but I go for 1mm diameter (of the copper, not the plastic).
Did I mention you will need an inline fuse. I know you mentioned it on your last post (12v fused supply), but the relay will unleash the power of your battery and there is no opps button, unless you have an inline fuse between terminal 30 and the battery, then all is well. (On the terminal 85,86 side which connects to your current indicator another fuse is not necessarily needed. The indicator fuse will protect that part.