Big thanks to
@Ant-H for bashing around ideas and advice on what to try.
In the end it was two things.
One: the coin door ground wire was loose and shorting on the PCB in the cab!
I didn't even remove the harness so it means it was always loose! FFS honestly.
Two: The third jet was wired wrong. I thought as the two other coils were wired one way, the third would do the same.
I am utterly relieved it's all working.
I have some remaining issues to resolve.
* The left gate is on reverse and is stopping orbit shots.. d'oh
* The right flipper needs tightening down. I had to change it out as the old one was knackered. Looks like I didn't tighten enough.
* Jets/poppers need some adjustments to make them more sensitive.
* I think I burnt out the led candles for the dead heads. Need to check on them.
I'll attempt some fixes tomorrow just honestly relived it's all working.
Also thanks
@Pick Holder for the advice. I did as followed, along with
@Ant-H advising the same.
It's definitely best to start with nothing into the board as it helped identify the short on the coin door area.