Quick update. I swapped the relays across and it still won't turn over for more than second or two. The battery was showing 13.33V. Should have a video below showing the non start.
https://youtu.be/XWWC5-ACFvgWhat happens if after its coughed you then crank for 30 secs?
Also switch the dash display to voltage and check whilst cranking it stays above 8 volts.
