Does anyone know what nitrogen pressure should be in a PS 420 shock?  PSI = ?

That is preset from the factory and should not be touched.

I am curious why you have not come back with any comments.
I hope you did not push in on the schrader valve and let the air out.
You know you have the  preload and  the  dampening settings. That is all you need. You cannot change the pressure.

"preset from the factory and should not be touched"  - Kawasaki would probably say that about most of the Concours. 

I bought a used shock that needs a rebuild so I took it apart to consider the task.  The bladder is rectangular, like a little pillow, and wraps around a cartridge unit.  With high pressures, I would expect the bladder to push the cartridge to one side so I'm curious how it was pressurized at the factory.   I would also like to pressure test it for leaks but am not sure what pressure to use.  It holds at low psi.

This is an odd shock with a steel cartridge.  There are no shims and all pressure reliefs are coil spring controlled like cartridge fork emulators.   

I believe the 420 is Gas Charged - not air.

I have one, it's great, but you dont get to mess with the schrader or the pressure

For any DeCarbon type shock, you should only use nitrogen to pressurize.  The pressure in the bladder is used to prevent air bubbles in the shock fluid.  As suspension tuners have become more experienced with this type of shock over the past 30 or so years they have found that somewhere in the 140 psi range is sufficient to prevent air bubbles and cavitation of the fluid.  You will need an anti-leak fill chuck and a nitrogen tank or you can take the shock to most any shop that works on dirt bike suspension and they will fill it for you for about 10 bucks.

Does anyone know what nitrogen pressure should be in a PS 420 shock?  PSI = ?

Like DM said, pre-charged from the factory.

That said, I have one on my '94, maybe 120k miles on it, rebuilt once by Progressive a couple of years back. The rebuild price was *VERY* reasonable, and they have all the tools, tanks, instruments, Faerie Dust, and a method for jamming ?? PSI of nitrogen into the shock before shipping it back to the customer. I highly recommend them.

Rick

"preset from the factory and should not be touched"  - Kawasaki would probably say that about most of the Concours. 

I am not sure what your saying. Kawasaki  has no say with regards to that shock.
That shock was manufactured by Progressive.  If you had a stock shock then yes, add air per Kawasaki.
Are you sure you bought a used Progressive shock? or did you buy a used  Concours shock?