Installing Aftermarket temp gauge

Hey guys I bought an temp gauge Amazon.com: MATCC 2 Inch 52mm 100-250 Degree F Car Auto Water Temperature Gauge Backlight 12V: Automotive and was wondering how I would go about wiring it. The instructions say to connect it to the ignition switch but I'm not sure how to reach that or if we can use an alternative. I was also wondering if a 1/8 sender would suffice instead of the one provided.