My 4X4 isn't working. The problem originally started by shifting into 4x4 intermittently, then if left in 4X4 position overnight it would engage when started up in the morning, now nothing. I have the 4.6 w/ manual shift. I'm getting 12v to vacuum solenoids @ the pass. side firewall, 8.5v to the switch on transfer case, linkage does engage the front driveshaft, diff lock vacuum motor stays @ unlock w/ vacuum holding it there. If when shut off I place the diff vacuum motor in lock position, it goes to unlock @ startup. It seems that the vacuum solenoids are not being energized properly, any ideas what may be causing this.

TIA
Dan