Black with a yellow stripe should be ground. There is usually only one ring terminal to the battery, so it should probably go to a bolt somewhere. If that wire goes to the starter solenoid then skip the rest of this and go straight to the last sentences.
If your starter is not working you will need to follow the wiring, something must be unplugged or plugged in wrong. I'm assuming when you say the kill switch is not on you mean it's in the RUN position, not OFF. The starter will not crank in the off position. There are a few other things that can interupt the starter circuit, there is a neutral safety switch on the clutch handle, and obviously the ignition itself. It's not unusual to have "extra" wires that don't go anywhere, my bike has a few on the top of the frame in the big mess of conenctors, and a few more in the headlight bucket that are not used. In the future, it's a good idea to grab some masking tape and just put a number on each side of the wire before you disconnect it so when you go to put it all back you just match the numbers up
Ok, some things you can check with the meter. Put it on DC volts, probably has a 20V setting. Ground the black lead. Take the red lead and with the key on, kill switch on RUN, check the lug on the ignition coil with the yellow/red wire. Should read 12V or so. If that is ok then the kill switch should be ok. (if you turn the kill switch to off the voltage should drop to 0)
Next you need to find your starter solenoid. It has the big red wire from the battery going to it. You need to probe the SMALL black wire. It should have 12V to it when the starter button is pushed and the clutch is IN. If no voltage there you need to trace that black wire. I think you will find the clutch switch is connected in the headlight bucket, the wire should be black the whole way. Should run from the start button, through the clutch switch, then to the solenoid. If by some miracle that checks out alright and you have voltage to the solenoid, then you are probably missing ground. On my bike I think the ground starts off as yellow/red and then later becomes black/yellow. If that is the wire you have in your hands that you dont know where to connect then you already found the problem