Disconnect the electrical connectors at the axle, then try a new fuse. This'll let you know if it's at the axle or somewhere up the harness.
I would go with the cable system.
When you need 4x4 you need it......The Thermal systems are sketchy at best...
POSILOCK comes to mind.
Probably a dead short somewhere, or the thermal element itself. Good luck finding it.
You have alternatives. Update the diff to a modern
Installed new DORMAN 600-100 Actuator (Thermal type) in 2021. Used 4-WD. once or twice since. New fuse blows as soon as key turned "on". Obviously
The Munz 01-29-2023, 21:59
'94 K2500 keeps blowing 25a front axle engagement actuator fuse(s).
Instead of a fuse, stick a test light in the fuse terminals. When you activate the 4WD, if it lights brightly you have short. And, you can re-use the
JohnC 01-31-2023, 15:24