Where is the oil sending unit on a 1979 Chevrolet C10?

The oil pressure sending unit on a 1979 Chevrolet C10 is located on the driver's side (left side) of the engine block, near the oil filter. It's a small, usually one-wire, electrical unit that screws into the engine block. The exact location might vary slightly depending on the specific engine (small block V8, big block V8, inline 6), but it's consistently in that general area.