Oil pressure gauge install information for disconnect.

[ratman90]

I'm putting in a new oil pressure gauge on my 72 C10. I was reading about the disconnect Union just outside the firewall on the engine side to make it easier I guess if the engine is pulled?

What exactly is the purpose here and what parts would I need?

Is there a way to put a tee in it to have the oil pressure light light up as well? Or even run a disconnect for the ignition if there's a loss of oil pressure.