4 wheel drive problems


I have a rocky F73-F78 V reg. I cannot get the 4 wheel drive light to switch on or the gear to engage the front axle , there is power to the cab switch and when pressed does seem to actuate a relay but nothing else is visible, no lights on the dash or in the switch, I do have vacuum at the gear box end and all connection seem to be clean ,any ideas as to the problem?