  We present an {\it ab initio} analysis of electron conduction through a
$C_{60}$ molecular device. Charge transfer from the device electrodes to the
molecular region is found to play a crucial role in aligning the lowest
unoccupied molecular orbital (LUMO) of the $C_{60}$ to the Fermi level of the
electrodes. This alignment induces a substantial device conductance of $\sim
2.2 \times (2e^2/h)$. A gate potential can inhibit charge transfer and
introduce a conductance gap near $E_F$, changing the current-voltage
characteristics from metallic to semi-conducting, thereby producing a field
effect molecular current switch.
