To find the correct wire, you'll need to:
* Consult a 1978 Corvette wiring diagram: This is the most reliable method. A factory service manual or a reproduction wiring diagram specific to your Corvette's engine (likely a small-block or big-block Chevy) will show the wire color and its connection to the oil pressure sending unit. These diagrams are available online from various sources, but be sure to get one specifically for a '78.
* Trace the wire from the sending unit: If you can access the oil pressure sending unit itself, you can carefully trace the wire back to its connection point in the harness or on the engine.
* Use a wiring diagram and a multimeter: With the engine off, you can use a multimeter to test continuity between the sending unit and various wires in the harness. Refer to your wiring diagram to identify potential candidates.
In short: Don't rely on a color alone. Use a wiring diagram to be certain.
