Thanks for the thougts Gav.

As I see it though, path to ground when 10 point card reel is at '2' is only to 20 relay .
Path to ground for player bust relay is if
a) A player relay is not activated (which is in single player mode) and No 8 or No 9 relay is activated (at 18 or 19 repectively.. which I've checked work correctly) and Rollover relay is activated and 10 pt card reel is at '3' .. ie 30.

or b) either 1 point card reel is at '2' and 20 relay is tripped.

Even if 10 point card reel is at '2' (20) and 1 point card reel is at '0' and A player make/break switch is not open on side to 1 point card reels, the path to ground (to bust relay) is via No 8 or No 9 relay and rollover relay switches.
As I've said earlier.. I have checked that when 10 point card reel (checked both reels) are at '2' there is no ground on position 3 and when either one point card reel is at '0' there is no ground on position 2 or above.