How can I test for voltage on the electrical motor for 2WD and 4WD that is on the transfer case?

Usually, it is the transfer case motor that is bad which will cause the vehicle to stay in 4wd but here are the wiring diagrams so you can check for power and ground, and I have included the instruction on how to change the actuator out for a new one in case you need it. This guide can help you check for power and ground. Also please check the fuses before you begin.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Check out the images (below). Let us know what happens and please upload pictures or videos of the problem.