Where is the oil pressure sending unit located on a 1989 Ford Ranger?

The oil pressure sending unit on a 1989 Ford Ranger is located on the engine block, near the oil filter. It's a relatively small unit and often has a single wire connected to it. You'll likely need to look closely around the oil filter to find it. A shop manual or online diagrams specific to your engine (2.3L, 2.9L, or 4.0L) will be very helpful in pinpointing the exact location.