Teething Troubles
So I turned the machine on to see if it would work having completed the playfield. It was no surprise that it did, as I had been regularly checking the functionality of the machine as I added the bits and pieces. But one thing kept re-occurring and that was that the machine kept on resetting itself.
It turns out that the CPU board was loose and by moving the board the resets were happening. I tightened the mounting screws and the resets happened less frequently, but still happenend. A bit of judicious prodding later established that the problem was infact with the ribbon cable going from the CPU to the power board. Having unplugged and reconnected this plug several times, the problem went away.