Here we see the MD-80 autopilot, All LED is controlled by the Open cockpit display card. In the image is the auto throttle and the auto pilot switches witch are circuit breakers that can be electrically disconnected. This is done via 2 relays mounted on Open Cockpit Master Card output using a optocoupler. Reset is done by shorting circuit the breaker with a separate power supply. Untraditional, but it works. Read more about the construction here: http://www.md80project.dk/portal/files/downloads/Panel/ATAP.pdf