How does the front differential actuator work? I'm troubleshooting my 4x4 system, as it makes crunchy noises up front when trying to engage.

The vacuum system is good, I replaced the check valve, and when I tested vacuum to the actuator it did the following:

When vacuum applied to nipple facing rear of truck, rod moved into the differential. When vacuum was removed, rod came out of the differential.

When vacuum applied to nipple facing towards the differential nothing happened.

I'm not sure if my issue is mechanical or electrical. I swapped the solenoids from my parts truck with no change.

I'll go though the wiring diagrams tonight for the electrical portion.