Thanks for the responses.

Here is the specification of the amp:

12V TRIGGER OUT: The +12V TRIGGER OUT is used for controlling external equipment that is equipped with a +12V trigger input. This output will be 12V when the C 356BEE is ON and 0V when the unit is either OFF or in standby. This output can drive a load up to 50mA at 12V.
TRIGGER OUT
Output resistance 75 ohms
Output current 150 mA
Output voltage +12 V ± 10 %