What about this then? 
Group gOutdoorCar "Pulpo XC60" ["Car"]
Group gCarLock "Pulpo XC60 Schloss" (gOutdoorCar) ["Lock"] {widgetOrder="05"}
Switch CarLocked "Verriegelt [MAP(de.map):%s]" <lock> (G_jdbc,G_Car,gCarLock) ["Control"] {channel="volvooncall:vehicle:pulpo:doors#carLocked", alexa="LockController.lockState"} // Problematic channel on 2.5.5 VOC binding
Contact CarDrFrLeft "Tür vorne links [MAP(de.map):%s]" <car_doorf> (G_jdbc,G_CarDoors,gOutdoorCar) ["OpenState"] {channel="volvooncall:vehicle:pulpo:doors#frontLeft", widgetOrder="06"}
I have my car’s lock (sub-equipment group gCarLock) in my car (equipment without location).
The lock is a Group within the Car group (gOutdoorCar) with a switch as Control.
If I check my Device / Equipment on the overview page, I can see cars → my car, but within there I don’t see a lock - neither as the Group lock, nor the switch lock. (also not as a badge on the Cars Equipment, as I assume it’s available on locations only).
According to this, sub-equipment is possible: