'94 fullsize Blazer 4WD won't engage

I installed a new actuator 2 yrs. ago in my '94 full size Blazer (lever shifter)along with the new wiring harness (Chevy changed the actuator from 2 to 3 wire) and everything was fine until 3 weeks ago. Preparing for a snowfall, we hooked up the snow plow and checked the 4WD and all was well. Six hours later we went out to plow and had no 4WD and still don't, with or without the plow mounted. I'm not sure where to start without wasting a bunch of time and money and now we're looking at a possible snowfall tonight.
I always wondered what it was like to procrastinate but never got around to it. Any help would be greatly appreciated and HAPPY NEW YEAR to all!
Mike