How do i know my booster is gone bad and my abs light is on

one of your sensors has gone bad or its connection

bad brakes. (do explain tighter?) (to a blind, no leg man)
first fix bad brakes, then worry ABS. last
explain tighter.
in driving school , they teach , how to drive (safely) with a stalled engine
as the engine stalls. and vacuum hits zero, the booster slowly
dies and bingo , old fashion , manual brakes. (stalls are like that)
is that what is happening. engine stalls?, or the booster is failing?
what happens there is brakes are 100 ok, but just harder to press
the pedal so you press harder and brakes are ALL THERE.
the is all by DESIGN.. no accident (no pun)
see if you have any other bad brakes symptoms.
like these.
http://www.fixkick.com/brakes/brakes.html#DoNotDrive

if brakes are 100% ok then , run the ABS scan or diagnostic
stated in the FSM , see what code you are getting.
then post that. ABS can not function correctly with bad brakes.

A vacuum leak to booster, a bad booster and last bad switch at brake pedal, again dealer must do control module calibration or light will flash indicating calibration is needed.

This sounds like the abs system is coming on, this may be due to a bad wheel sensor, the best way to see if the noise is the abs is to remove abs fuse and drive, the abs light will come on but drive to see if noise is gone. by removing the fuse the system will shut down. the way it makes noise when close to a stop means the abs could be the noise, a bad sensor at the wheel would cause this. it looses the signal for a sec or two and the compuetr thinks the wheel is skidding and the rest are moving, so the noise you hear is the abs unit release the wheel. if the abs is the problem then the next step is to have a garage scan the abs module for codes. the codes will tell you where the problem is and which wheel. good day.

go to some on eles and have them scan it. but i thank your abs pump is bad or its brain. also brake booster can cause the pedal to be hard if it is bad you should be able to hear a hissing sound in side the car when you push the pedal

Suspect your booster valve failed open, but not sure the ABS system is working right either. You can test the booster by checking to see if it will do it again in park. If the booster is bad, you'll need to replace it. Then, I'd see if the lights will clear. If not, suspect ABS computer is bad, but I'm not an ABS expert.

Do you by any chance hear a hissing noise from under the dash? If so, yes, you have a bad booster. For it to do what you're saying, it would almost have to have a vacuum leak. However, if there is a problem with something in the ABS system, you should have an ABS warning light on. Also, ABS can make the pedal fade, but I've never heard of it making the pedal hard. Your diagnosis of a brake booster does sound likely, but I'll admit I can't be sure -- this is an odd one.

A bad brake booster will result in a hard brake pedal, stiff and more effort required to stop the truck. Here are my questions to you, first, you said you replaced the master cylinder, did you bench bleed it before you installed it? If not, there IS still air in it, regardless of how much you bleed the brakes at the wheels. Second, when you bled the brakes, after changing the calipers and master cyl., did you also bleed the proportioning valve? Sometimes air can get trapped in the valve, and its almost impossible to get it out bleeding just the wheels. And lastly, when the brake light comes on, does the abs light also come on with it? Air can also get trapped in the abs control module too.

yes your booster or abs system is bad booster is about 200 plus labor your abs system is probally in the thousands

You problaly need a new front hub assy. They have the abs sensor built in. You need to see what code you have for the ABS and it will tell what you hub is bad. Don Suzuki tech