4WD Problem '99 Blazer - Front not engaging (found reason)

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I had a problem with my '99 S-10 Blazer 4WD system. When I would push the Auto, or 4-HI, or 4-LO button it would blink for a minute, then go back to the 2-HI light. It would shift the transfer case into 4-LO using 4-LO button, but front would not engage (you can feel this when turning).
Under the battery there is a vacuum driven cable that goes to the front axle, which I tested with a hand vacuum pump. Worked ok.
However, I found no vacuum there when button was pressed (engine running of course). I traced it to a small solenoid above the distributor mounted to the firewall. Other side has engine vacuum. It got 12-volts when I pushed a 4WD button, but it would not allow the engine vacuum to go through.
It is vented by a small hole on top and dirt/water can get in there and gunk it up, which is what happened. $50 at Chevy.

Note: All 4WD button lights come on as a test on start.
Note: Switch to 4-LO need trans in neutral and either stopped or very slow coast (recommended).

Good luck.
Larry