[road_rascal]

According to my 2001 Ford Service CD there is a sensor at the bottom of the tank. This is what the CD says to do to check it:

Measure the resistance between the low washer fluid level switch C117 pin 2, circuit 1303 (GY), component side and the low washer fluid level switch C117 pin 1, circuit 1205 (BK), component side, while the reservoir is empty and with washer fluid in the reservoir. (pins on the sensor switch)

Is the resistance less than 5 ohms with the reservoir empty and greater than 10,000 ohms with the reservoir filled?

If no:
INSTALL a new low washer fluid level switch. TEST the system for normal operation. (I would guess this would be the answer)

If yes:
1 Disconnect all instrument cluster connectors.
2 Check for:corrosion, pushed-out pins
3 Connect all instrument cluster connectors and make sure they seat correctly.
4 Operate the system and verify the concern is still present.

Is the concern still present?

Yes:
INSTALL a new instrument cluster. REFER to «Instrument Cluster» in this section. CLEAR the DTCs. REPEAT the instrument cluster self-test.

No:
The system is operating correctly at this time. Concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.