"Thanks all, I just connected the LIDAR through PWM. That seemed to work following the same steps as the v2 outlined in the ArduPilot documentation. Make sure your PWM rails are powered on the pixhawk if using this method! "

"Hi Martin, are you running the latest stable version of your firmware? I'm currently running ArduPlane 3.7.1 and I have no option to set RNDFND_TYPE to 15, LidarLiteV3-I2C.  Martin said:
Late but worth adding. Had issues working out correct…"