Four way brake union

That is the brake pressure warning switch. It is in parallel with the parking brake switch, and when either is grounded it activates the warning lamp on the dash. It should not be difficult to find, it has a plastic connector that fits over the stud on the switch

What year/ make / model are we working on?

You can download free factory service manuals and 3rd party aftermarket wiring diagrams, at MyMopar