On our old -200s the ADP would run continuously (obviously when there was air) when the switch was positioned to AUTO and the left MLG door was open. The auto function activated through the open door lock. I accidently discovered this when pressurizing the C system to shut the door after checking the inclinometers for a fuel drip.
There was a SB issued about 10 years or so ago to provide continuous ignition when flaps 1 were selected. Prior to this we had to remember to do it manually.
Cheers.