When In 4hi Or 4lo The Front Differential Is Not Engaging.
The 4wd Engaged Light Is On In 4hi And 4lo.
In 4lo The Transmission Is Definately In Lo. I Need Input
Thanks Dan

How do you know it's not engaging?

How do you know it's not engaging?
because the rear differential is the only thing engaged and i can't push snow with just rear wheel drive it's one of my plow trucks.

Do you have manual locking hubs?

You have a problem with the central axle disconnect. Get under the truck, and check on the right side of the axle housing. You will see a unit there with a couple of vacuum hoses running to it. One is vacuum, and one is a vent hose. start there, apply vacuum to the disconnect, and see if it tries to shift the collar. if it does, trace your vacuum lines back to the source, and you will find your problem.