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Sunday 24 December 2017 at 20:46
Smirnoff-if you're not familiar with Williams score motors, the stacks actually start with "Index," which is tall and (usually) closest to the front, then goes 1-2-3 ..
Loosen the two screws on it so you can get in with some flexstone or fine sandpaper and a swab and alcohol. Check that the contacts...
Source: http://pinside.com/pinball/forum/topic/williams-grand-prix-bonus-issues#post-4140936