Replacing Vacuum actuator(switch?) for 4WD Automatic tranmission

What is the easiest(DIY)way to replace the Vacuum Actuator (switch?) in a 1995 Chev Blazer with an Automatic Transmission,4WD?

Purchase service manual for your Blazer.

Follow directions in manual.

Where is the switch located? It’s located on the center of the firewall behind the distributor on my 2000 Blazer with Autotrac. I believe it’s mounted on the transfer case for Controltrac systems.

If it’s on the firewall, disconnect the vacuum hoses, the wiring harness, and unbolt it from the firewall. Install the new one, connect the hoses and the wiring and you should be good to go. To verify the switch is bad disconnect the vacuum hoses from the switch and connect them to each other. If the 4wd light stops blinking and the Blazer goes into 4wd the switch is bad. A picture of the switch is in the attached link. This link helped a lot when I was troubleshooting the 4wd on my Blazer.

The Vacuum actuator (ball shape with rod coming out) is mounted under the battery tray. Also check the vacuum lines for leaks and rot. has an online manual for the Blazer.

Ed B.