The 4WD light in the cluster is fed +12V along with the other warning lamps, and to turn it on, ground is supplied by the 4WD controller via an orange/black (orange with black tracer) wire, some vehicles had a standalone 4WD controller (mounted near the accelerator pedal), others had the 4WD controller integrated into the ECU/PCM, the input from the transfer case to the 4WD controller is a black/orange wire - just connecting the two together should allow the light to work properly without the pump in place.