Unable to Engage 4 Lock or 4L

[RussH]

Hello, I've just acquired a 2007 Grand Vitara. It's been really well looked after and drives great. However. I can't get it to engage 4 Lock or 4 Low.
The selector moves just fine, but no lights on the selector or the dash. I've tried doing it stationary, moving slowly in neutral or in gear.
I've checked all the fuses.
I doubt the previous owner ever tried to engage the centre diff. or put it in 4L.
I've tried searching the forum and Google but haven't got anywhere. I haven't even found any information on how it actually operates. Is it an electrical motor, vacuum operated?
Any pointers gratefully received. I'm pretty competent with this sort of stuff but have no knowledge of this system.

[donkeychomp]

It may well be in four wheel drive but the bulb has blown on the dash. Have you checked to see if all the wheels are moving?

[RussH]

Thanks for the reply, it's got power to all 4 wheels.
But I can't get it to lock the centre diff. Or select low range.
No warning lights appear on the dash, either when you turn the ignition on or when you turn the selector knob.
It seems dead. The previous owner had been jump starting it so I'm guessing he may have tried the 4x4 control unit. I've found some info about how it operates so I'll start testing for volts at the control unit and actuation motor.
I tried connecting a scanner but it wouldn't communicate:-(

[RussH]

All sorted:-)

A mouse had been munching through the wiring harness.