No 4wd light

I did some digging and seemed people were having different 4wd issues than me.
I push the 4wd button and the 4wd icon never comes on. I tried from a stop, neutral, rolling slow, all of it. The light never comes on. Could it have anything to do with the type of fluid in the diff? I think the previous owner used Amsoil in it. Is there a 4wd fuse? Thanks

No 4wd light

I did some digging and seemed people were having different 4wd issues than me.
I push the 4wd button and the 4wd icon never comes on. I tried from a stop, neutral, rolling slow, all of it. The light never comes on. Could it have anything to do with the type of fluid in the diff? I think the previous owner used Amsoil in it. Is there a 4wd fuse? Thanks