Isolator solenoid: With the engine off and key on have someone push the emergency start button and see if you can locate it by sound.
Then with the engine running several minutes (for any electronic delays) measure the voltage on the coil terminals which should be 12V. If you have 12V then measure the voltage across the battery terminals on the solenoid with a digital voltmeter. It should be very close to 0V, maybe 0.1V.
Some electronics detect battery voltage and engage the isolator only as required. With charged chassis battery and discharged house battery the solenoid should engage. Some systems are simply ignition on and the solenoid is engaged.