in my 96' 4runner i cant get my rear diff lock to engage. any thoughts on what is causing this

 

It's common for them to sieze up if you don't use it for a while. Try backing up and going forward a few times. You could try to tap on the motor with a hammer too.

 

your diff lock only work in 4low unless you have done the mod. also try engaging it and steering left and right as you're driving forward. the wheels need to be at a certain position relative to eachother for the locker to engage. hope this helps.

 

Put in 4lo, engage locker, and drive in circles for a few minutes. Stopping every once in a while and going the opposite way.

My buddy bought an FZJ80 w/ dual lockers that did not engage. We did this afterwards and both now work