I very much doubt the QM or Grenadier is wired like an aftermarket install of the Eaton E-Locker. My assumption looking at the diagram and if the BCM/diff lock module is controlling a relay and not directly connected to the diff lock coil. The ignition supplied through the switch to 86 on the relay will likely be a constant ignition power through a fuse through the relay coil. 85 will be connected to a BCM or diff lock module and switched to ground within the BCM/diff lock module, however this could be opposite and the BCM diff lock module switches power to the diff lock relay. The BCM control for the diff lock will be ignition controlled and have the information from the other systems that will enforce the logic for diff lock engagement, like center lock engaged, low range, engine running etc and the feed backs. The ground for the 8amp diff lock coil will likely have its own ground so not to spike the BCM/diff lock module when the lock switches off. There will be a diode across the relay coil to protect the ECM. Assuming there is a diff lock relay you could give relay pin 86 for the relay a new switched power source and pin 85 ground a new ground disconnected from any ECU control and have the diff locks work like the aftermarket diagram.
