Fuse jumpers are used in conjunction with the E-Timer electronic ignition to bypass (short out) the coil points and condenser (capacitor) on Model T ignition coils.  The E-Timer takes over the responsibility of charging and discharging the ignition coil to generate a hot, precisely timed spark for optimal engine performance.  The coil points will still vibrate and buzz providing the sound and appearance of stock operation but the condition and alignment of the coil points no longer determines the quality of spark.