After the backbox and cabinet are reconnected, nothing on the electro-mechanical game works properly.

EM game acts crazy after reconnecting head plugs

Cause: A head-to-cabinet plug (Jones plug) has been pushed in reversed or into the wrong mate.

Checks

• Each plug is normally a different length with a different wire count; the female half on the backbox has a metal tab that blocks reversal.
• Compare the wire colours on each male plug with the colours on the female it is in; they should match pin for pin.

Fix

• Unplug and refit the plug the right way round; a reversed plug does not damage the game.
• Mark or colour-code look-alike plugs before you separate them next time.

Systems

• Electro-mechanical

Related tips

• EM game worked before the move but not after

Source: Pinball Machine Care & Maintenance, Bernard B. Kamoroff (Bell Springs Pinball Alley)