Are you sure you got the gear put back in the right place? If it was put back in a little off kilter the computer may not be able to read its position, therefore the light won't come on and it won't shift into 4x4.
To test the power you will need a DC power source such as a battery or battery charger, and you apply power to the yellow and orange wires coming out of the cylinder area of the motor. I would recommend taking out the circular gear with the bump stop on it and just testing to make sure the motor spins. To get it to run in the opposite direction just flip the positive and negative wires. Then after you are sure the motor turns without binding or anything, I would put the circular gear back in and then test it once it is put back together. Be sure before you put it back on the truck, that the gear is in the same position as you took it off in.
This is all I had to do to get my motor working again along with replacing the bump stop. Hope it helps.
