No Reverse transmission

I have a 89 jeep cherokee with six in-line 4.0L. The automatic transmission is not getting the reverse. All the other gears work fine and have no problems its just not getting reverse. Is there an sensor or electronic thing that would control the reverse?

First thing that I would do is to make sure the shifter is aligned properly.

Then I would check for reverse lights to determine if the NSS is working.

Thanks for the advice. I did not check the NSS and double check the shifting cables. So if the light doesn't show in reverse the NSS is not working?