The 4 wheel drive in our 2006 Ford 150 is working on some days and not others, mainly when the weather is cold and snowy (when we need it)it won’t turn on. It must be a connection that is effected by cold or moisture?
Your post prompts me to ask: Have you driven on dry gravel roads or dry asphalt on days with the 4x4 engaged?
Most likely a vacuum problem.
Your truck doesn’t have free running hubs like the old days.
What it has is vacuum actuators at each front wheel. A collar & seal looking thingy which is connected with vacuum.
There’s a vacuum solenoid on the firewall and many little plastic vacuum tubes connecting it all.
The problem in the cold leads me to the wheel actuators prmarily.
Is there an easy way to diagnose this or is it better left to a pro?