Where is the coolant sensor on a 1988 corvette?

The coolant temperature sensor on a 1988 Corvette is located on the cylinder head, near the thermostat housing. It's a single-wire sensor. There might be multiple sensors in that area; the coolant temperature sensor is usually the smaller one. You'll need a service manual or a diagram specific to your 1988 Corvette's engine (L98 or a different variant) to be absolutely certain. A visual inspection with the aid of a diagram will be the best way to identify it.