Dead tach and no backlight

[bonestock87]

My tach sits with the needle pointed at 6,000 rpm and there's no backlight behind it. Where should I start checking to see what's wrong? I don't know if this is related, but there's an unplugged sensor hanging down next to the transmission and I haven't figured out where it plugs in. It seems like it's coming from the engine bay.

Thanks!!