A retrofit turner and sensor unit includes, on its upper portion, a grain turner for moving grain from a central portion in the grain pathway to a defined outer space for measurement. On its lower portion, the retrofit unit includes a moisture sensor and a temperature sensor provided in a plate configuration in line with the outer wall of the grain dryer for sensing moisture and temperature of grain in the defined space. In the preferred configuration, the plate sensor includes redundancies, and is mounted on a hinged door. The retrofit unit is easily installed into an existing grain dryer with columns and continuous flow capabilities, and electrically connected with a controller/processor and a motor for metering rolls which determine grain speed through the dryer.