1995 Isuzu Trooper Master Cylinder

If there's no actual leak within the brake system-double check the brake master cylinder could be defective regardless if its new-

How would you check it?

Remove the brake lines from the master cylinder and plug it-then apply pressure-if it sinks in half way-you've found your problem

I was unable to get something to block the brake line holes. I have taken the master cylinder off. After looking at an online diagram at myisuzuparts.com of the master cylinder, I noticed that 2 parts are missing. What the diagram calls a retainer frt shell m/vac, and the seal m/vac. Do these parts typically come with the master cylinder?

I have gotten a new master cylinder and the brakes felt better. Then I turn on the car and the brakes still go to the floor. Is there a specific sequence in bleeding the brakes, Am I missing something else?

Check the calipers/wheel cylinders if they're leaking if not bleed the brakes from RR/LR/RF/LF

That is the same way I bled the brakes.. I got lots of fluid and little to no air. While the car was off the brakes felt firm, then I was going to take it for a test drive and turned the car on. The brakes went to the floor and the rear abs and parking brake light came on. After checking the lines again I got discouraged and went to search for other things online about the brakes. I went back out and started the car.. the lights are off, the brakes still go to the floor, and there is a loud clicking coming from the shifter when I apply the brakes. Thoughts?

Check the ABS unit