On a 1986 Chevrolet C10 pickup with a 305 engine, the oil pressure sending unit is typically located on the
passenger side of the engine block, near the
front of the engine. It's a relatively small unit with one or two wires connected to it. It's often near the distributor, but not always directly adjacent.
It's best to consult a repair manual specific to your year and engine for a precise location with a diagram. A visual inspection, after ensuring the engine is cool, will confirm its position.
