The main problem with Gottlieb System 1 games is that the grounds are not
solid. All the grounds in the machine are attached to a grounding strip on
the bottom of the main cabinet. The problem with this strip is that the
terminals were just pressed on. Solder all the grounds solidly to the strip
so prevent the floating ground problem. This will prevent all sorts of
wacky behavior in your Gottlieb System 1 games.
Tim Arnold pinGame journal, #25 September 1993 pp 37.