Koletrain

I have replaced the actuator on the front diff. You can hear the transfer case engage into everything fine. After replacing the actuator I saw the 4WD fuse inside the cab fuse box was blown. I replaced it. Tried to engage the four wheel again with the new actuator and fuse still nothing the front drive shaft will spin when in four wheel. The front tires won't. And noticed after switching everything out (actuator and fuse) the fuse blew again. Any ideas where to start? This is all on a 96 GMC Sierra Z71