If you have the sensor, you'll have a second black thingy on top of the tank. One is the cover thingy that lets you fill it with stuff to squirt. The other thingy is the top of the sensor. Both thingies look similar, but are different. Sensor thingy won't come off like a cap thingy.
In this pic you can see the level sensor at the far forward section of the tank (through the CAI top cover):
The pumps are mounted on the sides of the tank lower down. Note that this is a double-tank for 92-95 SSE/SSEi with headlamp washers. But any other GM car with a level sensor should have a similar or identical sensor on the top of their tank.
SENSOR: 2 wires only.
PUMP(*): Wire harness AND fluid delivery tube.