Why won't my brakes bleed on my 1990 Jeep cherokee

You have to bleed the mater cylinder first then the lines...Bench bleeding is the best option. If you were to try this with the brake lines attached, you would push large amounts of air into the brake lines, and it would take a lot of time and effort to remove all of the air from the master cylinder. You would end up fighting spongy brakes for weeks

https://www.youtube.com/watch?v=kEPXgDGU6_0