When I restored my STTNG I had a similar question
@Jay Walker responded with the solution. I decided against enabling it. I suspect as its a Williams of the same era that the issue was the same.
cmrl9 said:
Noticed the "Special" coil top left is not connected, any ideas where this is suppossed to go?
Hello,
That coil in the top left corner is the 'Knocker' solenoid. It looks like your machine is using the drive circuit for it to operate a coin meter instead. I spy the matching connector for it in the picture, peeping from behind the edge of the display panel. The production line would connect that plug into the knocker or the meter socket as required. Assuming that you wish to use the knocker, separate the connector as it is and plug it into the wiring of the knocker. Be thankful the knocker is still present; it's the same assembly (bar a return spring) as the left outlane kick-back.
However, the driver circuit will still need to be set to use the knocker. The quickest way to do this is to establish 'usa' settings, which have it pre-set. If the cpu board had an 8-way switch unit instead of those White zero-ohm jumpers (in a row next to the ribbon cable at the l/h side) you could set usa easily by altering which switches were On*, but with jumpers it's awkward. I've heard that having more than one removed/cut (equivalent to switches being Off) also sets usa, but can't vouch for this. In any case, altering the pattern causes a complete reset of the machines' settings and totals, highest scores, etc.
I unpacked games of this age new, and used to set knocker use while installing works' pricing scheme. The specific adjustment for knocker or meter is in the Pricing Adjustments, A.3., though it may be hidden unless a 'Custom' scheme/door is selected. It's called "Coin Meter Units", and is at the very end of the A.3 adjustment items. For the u.k. production (which this machine seems to be) it'll be '0.10'. It has to be Off to use the knocker.
* as I recall, the usa pattern is all switches ON/all jumpers installed (one's missing on this board)