Where is the oil sending unit located on a Blazer with 4.3 L?

The oil pressure sending unit on a 4.3L Chevy Blazer is located on the driver's side of the engine block, near the oil filter. It's usually a small, single-wire sensor screwed into the engine block. However, the exact location can vary slightly depending on the year and specific engine configuration. You'll likely need to consult a repair manual specific to your Blazer's year and model for the precise location. A picture or diagram in that manual will be invaluable.