hello to everyone
I've got a question concerning the 4x4 system on my truck. I've got a 95 K2500 6.5 TD, still with the manual selector on the floor to choose neutral, 4High , 4 Low or 2 high. When checking if everything worked as snow was coming my way, I put the truck on four stands, all 4 wheels free and put the selector in 4high, trans in D. Rear wheels where propelled, front wheels did not move!! The ingoing axle in the front dif was turning, but that's all. I did see two connectors and a huge solenoid on the front axle, but as I don't have any documentation on my truck I'm in the dark (or just plain stupid )

Here's the solenoid

Could anyone tell me something about this please?

Bye to all Gerard