The plunger under the battery is the 4wd actuator to your front differential to lock the axle to you have 4wd. you hooked the vacuum line back to it, but did you check to see if the actuator works. Engage the 4wd and inspect the actuator and see if it work, it should pull on the cable that connects to the front differential. It's common for the older 4wd's actuator go bad by a cracked diaphragm and not being able to pull on the cable to the differential. The other thing to is to inspect the vacuum line from the transfer case, it's located on the drivers side on the transfer case and connected to a vacuum switch. Check these simple things and replace any parts damages and keep me posted. be glad to help you get your 4wd working again.
