Front differential wiring and synchronizing?

I am trying to locate a 12-volt supply which is triggered only after the NP246 transfer case is ready for the front differential to come online. I believe the T-Case must lock in first prior to the front differential.
Here is the reason I need this. On my 2001 GMC Safari AWD, I swapped out the OEM AWD transfer case NV136 with a NP246 and all wire harness from a donor Silverado. To free up the front axle for smooth turns and reduce wear on the T-Case I installed a T-Case that is vacuum actuated off a 2003 Chevy S10. The vacuum is only supplied to the actuator when vacuum is applied to make the front right axle live when 4wd is commanded. For this to happen an electric solenoid is connected in series with engine vacuum source. It is turned on when 4WD is asked for. I need a 12v source that is controlled by the TCCM or directly from the transfer case. There is 4 wires ready to plug into the Silverado's front differential actuator motor. Here lies the problem, the S10 front diff is locked in via vacuum actuator.