Where is the oil pressure sending unit 1998 ford sport explorer?

The oil pressure sending unit on a 1998 Ford Sport Trac (note: not Explorer, there's a difference) is located on the driver's side of the engine block, near the oil filter. It's a small unit with a single wire connected to it. You'll likely need to consult a repair manual or online diagrams specific to the 4.0L or 4.6L engine (whichever is in your Sport Trac) for a precise location. The exact position can vary slightly depending on the engine.