The excitation of the ML221 or FE221 Bridge Amplifier is set by an external resistor between Pin 5 and Pin 8 of the Bridge Amplifier's DIN connection.
While the Bridge Amplifier has a default excitation voltage of either 0V (Open circuit between setting pins) or 20V (short circuit), the MLAC11 Grass Adapter Cable has an internal resistor that will set this excitation properly for Grass Transducers.
To learn more about how to configure an ADInstruments' Bridge Amplifier for use with non-ADInstruments transducers, please review Pages 85 - 91 of the Front-end Signal Conditioners Owner's