Brigger.
The adapter lead on your bike for the battery should be twards the front of the battery. Its grey and hanging on to a cheap plastic connector by the battery box to the frame I think. You should see it with the side cover off.
Is part number 70270-09 for direct connect into the amp? Something special?
Part number 70270-04 is an additional harness to hook up extra electrical assesories.
Where is the placment of the Amp? Under the seat?
What you can do is strip the red and black wires from the amp to battery at the battery end. Go to the Hardware or electronics store. Pick up a connecter for the posative and negative that will fit around the bolts on the battery terminal connector. "Those bolts that you tighten the nuts down for the cables on yer battery"
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The connectors should be completely round to fit around the bolt. They have a plastic piece on the end to slide the bare wire in. Heat to shrink the plastic around the wire. Take off both nuts to yer battery terminals. Slide positive connector to pos and negative connector to neg with wire already attached around bolt. Put nuts back on to hold em tight.