The FAST electric field instrument has ten sensors, two on each of the four 29 m radial wire booms (at 24 m and 29 m) and one on each of the two rigid 3 m axial booms. All except the four outermost sensors can also operate as current collecting Langmuir probes. Similar instruments were flown on S3-3, ISEE-1, CRRES, Polar and Cluster. The instrument is designed to provide the following: a vector measurement of the electric field from DC to about 20 kHz over a dynamic range of 0.1 mV/m to 1 V/m with a sampling resolution of 0.03 ms; AC electric field waveform measurements up to 2 MHz with a sampling resolution of 32 ms; continuous monitoring of the dominant frequency and amplitude of high-frequency waves with a time resolution of 0.03 ms; measurement of the thermal plasma density (1-10^5 cm-3) and temperature with up to 0.5 ms and 1 s time resolution, respectively; measurement of the density fluctuations over a dynamic range of 0.1-20 % with a time resolution of at least 1 ms; measurements of time delays between different antennae with time resolution down to 0.03 ms; and wavelength measurements for frequencies up to 20 kHz using on-board interferometric techniques and multiple sensor separations. The FAST electric field instrument stopped providing meaningful data around 2002.