a) Disconnect the connector from the indicator switch and connect the connector terminals on the indicator side together.
b) Turn on the ignition and check that the indicator lamp lights up and the buzzer sounds.
2. Checking the sensor for water in the fuel filter.
a) Remove the fuel filter water presence sensor
b) Check for continuity between the connector terminals when the switch is in the "OFF" position (the float is down).
c) Check for conductivity between the terminals of the connector in the "ON" switch position (float in the upper position).
Resistance between terminals:
- Float in the upper position - 7-10 Ohm
- Float in the lower position - no conductivity
[The official source is on the portal toyotaman]