Outer Limits 4x4 Board

hi i have a 45 cruiser with 2h turbo motor a project i'v taken over was running fine with no oil cooler it just had a line going back on to its self at sandwich plate finally decided it was time to install oil cooler iv ran the lines mounted cooler but now i;m having oil pressure gauge not reading and engine shutting down within a minute of starting. iv checked oil level its fine got oil in cooler and lines i even just connected the two lines together and by past cooler if that would make a different's but didn't so i'm a bit lost on direction from here if anyone could help thanks

undo one end of pipe and crank to ensure oil is going thru.