It's the "Engine Stop Solenoid". It has a 10 second timer relay.
When you turn off your key, it immediately uses the fuel stop solenoid to cut the fuel (which then turns off the RTV) but I can't remember all the details of what this particular solenoid does. If I recall correctly, this solenoid sits just above the injector pump and is clearly visible when the cargo box is lifted. If you follow the linkage, you can see what's being engaged (or disengaged).