4 Wheel Drive Light Is On But Does Not Engage To 4 Wheel Drive

The 1998 to 2000 Mazda trucks with 4wd use vacuum activated front locking hubs to lock the front wheels onto spinning front drive axles. Try to jack up the truck off the ground with all 4 wheels in the air and then turn your 4WD on. If just the rear wheels turn, but you can see your front drive shaft spinning the front differential, then you have a vacuum leak and should start checking the hoses at wheel hubs back to their source. The sealed vacuum hubs could also be the trouble. To pin point the problem on my truck, the technician had to use a a smoke machine to see where the line was faulty. Sadly the dash light will come on anytime the 4WD drive switch is turn to the 4X4 Hi or 4X4 Lo setting (after coming to a complete stop and depressing the clutch and neutral for manual or park and depressing the brake for automatic). Hope this helps you with your trouble shooting.