4 wheel drive will not turn on when engine is cold but when it warm up it work

Hello, Since the only thing that engages the 4WD is an electric motor, it seems like it would be obviously a bad electric shift motor in the transfer case. However, the circuit needs to be tested when the vehicle is cold, so it can be determined if power is not going to the motor on demand. Do you have the tools and ability to diagnose the circuit?