1991 Jeep Cherokee will not crank over we have replaced the starter ignition switch and battery is good what should we replace next?

The celonoid can be tested at Autozone. It may have jumped time or faulty spak plugs. Check to see if you hear the fuel pump tick when you turn the key switch to start it.

Then check the fuse box to see if any fuses blown that would prevent something to run because that happened to me. I know this may seem weird but if your car is a newer model it probably has a "brain box" which is for a lot of thigs including sending signsls for thr fuel pumpp and many things to start or stay running.