I just installed a tether on mine a few weeks ago and I done a search and found this info:
Q#58:What’s the right way to install a tether kill switch?
A#58:While some people run both wires of a tether kill switch to the coil, and this does work, it may cause damage to the CDI. The best way to wire a tether (or pushbutton) kill switch is to use the handlebar kill switch circuit. When the black/white wire on the handlebar kill switch is grounded, the CDI kills the motor. All you need to do is ground one of the tether wires to the frame (or splice it to the black wire for the handlebar kill switch), and splice (see Q#59) the other wire onto the black/white wire somewhere.
Thats what I did and it works fine