(This story is not a riff on Trucks/Maximum Overdrive, but rather on the 1974 TV movie Killdozer! which was itself based on a 1944 Theodore Sturgeon short story of the same name.)
This is a sequel to The Cooler Out of Space, in which the last fragment of the Entity contained in the cooler temporarily escapes Bane and Finch, following the Miskatonic upstream until it arrives in Dunwich.
There, it possesses and animates an abandoned field harrow, and literally cuts a bloody swath across the Upper Miskatonic Valley, until it is cornered and destroyed by the investigators.