Four way brake union

Especially with a pickup, and some of the places some of them go, LOL, it's possible a branch/ stick hooked the wire and jerked it clear out of there or some such, or that a previous owner saw it dangling, could not figure out what it was, and just cut it off

I do not have documentation on the trucks. Only other suggestion is to "spy" a similar truck of that similar generation and get the guy (or gal!!) to open up the hood for you