I picked up a used K2, and installed it. Red and black directly to battery, and yellow to a switched power source that goes on with the ignition. I put a brand new Sandisk 256GB in, and the firmware is the latest version.
Strange behavior is that there is no blue light on the DVR which would illuminate the "wifi icon". I am able to connect my phone however, as it found the SSID and accepted the default password of "12345678". I went into the settings menu to format the card, and it appears to do its thing, and reboot the DVR. However when I reconnect my phone, it just says "Card Error". Tried again and again but no luck with the brand new Sandisk. I tried three other cards that work fine on my GoPro, and no luck.
I have even replaced the power supply, to be sure. I'm baffled at this point, and would love to get some suggestions from the good folks here.