I'm missing something when attempting this in Mach 3.

I have all the switches so they home into the front of the machine, to the left, with the spindle going up. I hit "ref all home" and they all hit their switches and then back off a tiny bit.

I have a kamikaze Z axis, and when running a g-code will often start out plunging up, or if it doesn't do that it plunges down several inches a minute or so into a carve.  I would like so when it goes up and hits the switch it stops instead of trying to crush the switch.

How do I do this?

Slow down the homing speed in homing and limits to 20% or less.

I have that set right. 

The problem is that it works fine while homing.  The switches stop it and work just fine.  It's when I'm running a g-code.  The switches don't stop squat.

have you set Home Input and Axis++,Axis-- Input to the same port and pin?

You can set Home and Limit switch to same pin.
During the homing cycle, switches are working as Home switches. In all other situations they are treated as Limit switches.

Thank you!

You're welcome!

Bummer, I did this, yet when the Z axis goes too high it still does not turn off, but screams as it tries to crus the switch until I hit the escape button. 

if you go to diagnostic page and hit your Switch manually, can you see M3++Lim Led changing status?

Bummer, I did this, yet when the Z axis goes too high it still does not turn off, but screams as it tries to crus the switch until I hit the escape button. 

You may need to make sure that all your "Soft limits settings" are correct first.
I set soft limits so that soft limits are triggered 0.1 inch BEFORE positive direction limit switches are hit  even though my shared limit/home switches are working.
Soft limits will ensure the motion will automatically slow down when it the near the limit positions. Also, a negative direction Z softlimit can can be used to stop long tools hitting the vise bottom or machine surface below the the spoil board.