2006 STX, 4.6L, auto transmission, Manual Shift on the Fly.

Problem: 4 High will not engage. 4 Low works just fine.

Trouble shooting I have done: we have a lot of snow currently so I tested 4x4 2H good to go, 4H No dash light will not engage drive test still in 2H, 4low dash light and engaged drive test very good. Isolated 4x4 vac solenoid checked vacuum checked good, checked lines for connections/cracks/damage none found. connected vac gauge inline with the solenoid selected 4H no change in pressure, selected 4L pressure dropped and 4x4 engaged. Moved on to electrical checked fuses removed and reinstalled also passed continuity check, checked relays in the engine bay inspected and swapped positions since they where the same part number. ops checked again with the same check as before 4H nothing 4L good to go.

My conclusion: change the 4wd manual shift position switch on the transfer case because manual electrical signal not being sent to 4x4 vac solenoid to engage 4H. I will order and see what happens. If anyone has had this issue please let me know the fix. I didn't see anything like this problem when I searched the threads.

Update: replaced switch problem remains however the 4H light will come on now when I move the shift lever to the side a little and 4x4 does engage. I will be looking at adjustments. If anyone is good with finding parts or has the information please share I have searched till the end of the internet lol.