Check the CAD, the diaphragm may be toast. just replace.
If it's vacuum (has hose) just apply vacuum.
The vacuum actuator is on the right side of the axle. The electrical switch is on the actuator. The vacuum switch is on the top of the transfer case.
The trans in a Dakota is not controlled by vacuum.
The vacuum actuator is either in the fender or under the battery. The actually diff actuator is on the back/bottom of the front diff. Mine (2000 blazer) is under the battery. It sucks to get to. If you check the actuator and it doesn't move at all, check the vacuum, if it's not getting vacuum, check the switch on the top driver's side of the transfer case. It sends vacuum to the actuator. It has three vacuum hoses coming off of it. It costs fifteen dollars at autozone and usually greatly improves the performance of the acuator.
This sounds like a YJ jeep issue, I eliminated the vacuum actuator by installing a heavy duty choke style manual cable attached to the vacuum actuator arm, that way I can lock the front diff when I wanted. Make sure you cap off the vacuum line, otherwise your engine will run poorly.
No, it is electric
On a Dodge Ram, it runs from the intake manifold, to the switch on the transfer case, to the front axle shift actuator.
Idle speed is not adjustable. If the speed is incorrect you have a computer, sensor, actuator, vacuum leak issue.Idle speed is not adjustable. If the speed is incorrect you have a computer, sensor, actuator, vacuum leak issue.
The actuator of the Dodge Ram 4x4 is located on the top of the front differential. Depending on the year, the actuator is either vacuum or manually operated.
on the front axel
Under your battery tray
Autozone web page has the Vacuum diagram for the1989 Dodge Dakota.