I recently had the same thing on a game. In my case it turned out to be a mis-adjusted switch 1A on the score motor. The way I found it was to use the wire with alligator clips (jumpers) to short across the various switched until the XB relay pulled in. so I had 4 or 5 jumpers in place (all switches except the ball count unit from memory) and then it would pull in the XB relay when I manually incremented the ball count. I then removed jumpers and activated the outlane switch until I found which jumper / switch was the problem.