Neither terminal on the low voltage side of the coil is grounded, so you'll have to use a different location. That mounting bolt toward the rear of the coil isn't grounded, either. I just installed a Vapor tach on my race bike, and it required a 600k ohm series resistor in the red tach wire to get a stable tach reading. You can get the cable with the 600k ohm resistor built in from Trail Tech if your kit didn't come with one. They sent it to me for free...
Since I removed my entire stock instrument cluster, I made all my connections to that square 9 pin connector--everything you need is in it. The ground wire is black with a yellow stripe, the tach signal wire is black, and the 12 V power wire is brown with a black stripe.
Also, be sure the Vapor unit is set for 1 pulse per revolution for use on the Ninja 250.
I can post some pics in a few days when I get back from racing this weekend.
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