I have a Moki 1.8 gas (same as RCS 1.8) - could someone explain to me what the black wire coming back from the plug cap is for? I have the battery connection made, but am at a loss on how to make it all complete.

Put it on a engine lug or put it on a bolt that is attatched to the engine...it's a ground...
IT's a gots to have...

The instructions say: "If you resite the integrated ignition system from the rear housing of the front induction engines to, for instance, the fire wall, then an earth-strap must be connected between the PCB and the motor itself (the igntion fixing bolts act as earth-straps as delivered)."

Is the black wire the "earth-strap"? Or do I need another wire?

WOW!!!!!

I can't even understand those instructions....

But the black wire is a ground..if in doubt run another wire like they say...

Hmmmmmm I had to read it again....
I think it means if you relocate the ignition to the firewall a extra wire will be needed..