97 sportsman 4wd

Hi folks,
I have a 97 Polaris sportsman 500 which has a problem with 4wd. When I bought it a few months a go the wires going down to the 4wd hub on the right side had been ripped out which I managed to repair but when I push the 4wd switch I get nothing.
I have tested the switch operation for continuity with a meter on the grey and grey/white wires and I am getting a good circuit (0.03ohms) when the switch is pressed so I know that is good. I have had a look at the wiring diagram but I’m struggling to see how it all works.
There are 4 wires to the switch, the grey + grey white for the switch operation, brown for ground and there is also a yellow wire. I assume this should be ignition voltage but I get nothing there and on tracing the wire through the harness it joins into the grey/white wire!?
Any ideas on this would be greatly appreciated.