My 4 wheel drive won't engage and I've changed the actuator, what's next?

This could be an issue with the actual switch. That is what tells the computer you have shifted into 4wd. You may want to test the switch and also test for power at the actuator. Alex

You'd be much better off having qualified personnel scan test the transfer case module to find the culprit instead of guessing at it and spending money on parts that aren't needed ! ▪️https://repairpal.com/repair-shops▪️