I've been messing around with this and I was going to do a bit of a write-up when I was finished. I've got mine working though so I can answer your questions at least!
my OEM harness has a positive battery wire AND an ignition wire. however the KOSO only states to have an ignition wire. where does this positive battery wire go?
There are two +12V wires, one from the ignition and one from the ECU. Use the one from the ingnition.
its three different wires, however. i assume one is a ground and the other is the speed sensor reading however i don't know what the third wire is or where to put it.
The Koso has three wires;
You will need to connect the positive 12V and signal wires to the speed sensor on the bike. The brown ground needs to be connected to the black ground wire on the Koso.
lastly is the tachometer wire. KOSO has an rpm wire, and my OEM harness has a tachometer wire. however, KOSO also provides a direct coil wire connection that plugs into the coils and then straight into the wire harness. i am not sure whether to do what KOSO tells me to do and plug straight into the coils, or to just wire straight to the OEM tachometer wire.
Just chop the connector off and wire it to the bike's signal wire that comes from the ECU, easy!
I managed to figure out the make and model of the connector (an MX34, 16 connectors by JAE) on the OEM clocks and then find a supplier that would ship less than 100 units. This meant that I could wire my Koso to the connector instead of straight in to the bike, like this: