Mack R600 1979 air lines to Splitter

Hi Mack men, I’ve got a 1979 R600. I took the cab off to give it a good clean up and paint. The cab is now back on, the truck starts and most things work. My problem is there seems to be no air at the splitter, it’s a 12 speed. Can anyone tell me where the air comes from to feed the splitter?
Any help would be much appreciated.

Here U Go

Try this on for size

www.bigmacktrucks.com/topic/13871-callin...ck-12-speed-experts/

cya

Thanks Swishy, brilliant information as always.