The connection will be the same as in the immobilizer scenario.
Link: Teltonika FMB Immobilizer Scenario - YouTube
But, Disable the Immobilizer in the device features, and do not use or connect any iButton Reader.
Just connect the DOUT of your device to the 4-pin automotive relay, then you need to send an SMS or GPRS command to activate or deactivate the DOUT.
In your case, you are using FMB920 which has 1 DOUT.
You need to send setdigout 1 to activate the immobilizer and setdigout 0 to deactivate the immobilizer.