'94 K2500 keeps blowing 25a front axle engagement actuator fuse(s).

[The Munz]

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 wiring and or harness or connector(s) or relay(?) etc. may be suspect. I've replaced 3 actuators since 2008 and I'll go a year w/o engaging 4-WD. Any suggestions? Thanks!

[DmaxMaverick]

Probably a dead short somewhere, or the thermal element itself. Good luck finding it.

You have alternatives. Update the diff to a modern stepper actuator, or a mechanical push/pull cable. Both are more expensive than replacing the thermal actuator, once.

[Robyn]

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.

This setup replaces the thermal actuator completely..........

When you engage the front end....It's in.....
You can also use the low range in the T case as a creeper gear on dry hard surfaces by leaving the front end unlocked.........

I have had the Thermal actuators fail when I needed it BADLY......Had to lay in the snow and replace it......

No fun...
The failure of a Mickey mouse gizmo in a MISSION CRITICAL PART is simply unacceptable.......

When the weather starts looking sketchy I have always taken the time to try the 4x4 in our GM RIGS to be sure they work....

Just because it worked the last time you used it....does not mean it will NOW...


Just my thoughts.......

As Maverick said....Good luck in finding the issue......Try unplugging the actuator and see if the fuse blows....

Look over the wiring the feeds the actuator and check for damage down around the axle area.....

The is also a switch on the T CASE that operates the system.....When the 4x4 is engaged in the case the switch activates the system.

May be the relay......But as mentioned...Sounds like a dead short.....

[More Power]

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.

As I recall from re-connecting the wiring on the 6.5 Blazer project recently, the front axle wiring passes across the top/back of the engine, sweeps around the back of the passenger side cyl head, then drops down along the starter before leaving the engine toward the axle.

The point where it sweeps around the back of the passenger side head is a tight spot where I spent some time getting the harness positioned just right, so it was protected.

[JohnC]

Disconnect the electrical connectors at the axle, then try a new fuse.

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 test light as many times as necessary.