Mystery Connection Near KickPanel

Working on my 1974 Dart Swinger and was looking for a 12V Constant source for my stereo install and came across this connector driver side under dash in kickpanel area, it has blue with white tracer. I've looked at the wiring diagram but can't figure out what it's for, any one know?
Thanks

Also would it be ok to connect a set of temp/oil psi gauges with the 12v switch radio wire? (tie all three to the red wire at radio connector)

Thanks again!