4wd issues

98 sr5 automatic 4wd with floor shifter. 4wd randomly went out, light not coming on. Checked fuse for 4wd, ok. Front drive shaft does turn when transfer case in gear 4hi or low. No 4wd indicator lamp and only pulls with rear wheels. What do I do.. I'm trying to learn how to do this stuff on my own but I'm stumped here. Also checked a plug going to the front axle, cleaned it up and still no 4wd. HELP lol

 

Pretty sure the front diff is vacuum operated, did you check the vacuum lines?

 

I have checked them to the best of my ability. Don't see any holes, cracks, or obstructions. The book I bought for the truck really doesn't help when coming to troubleshooting the 4wd. That's why I'm so confused on what to do.