Quoted from acebathound:Looks like the Aux Lamp Drivers use primarily [perhaps exclusively judging from the schematic] MCR106-1 whereas the regular Lamp Driver Boards use a combination of MCR106-1 (multiple lamps) and 2N5060 (single lamps). Maybe the MCR106-1 doesn't experience the same issues with needing the additional load resistor to prevent flickering as the 2N5060's. Or probably the more likely scenario, if the MCR106's are there to drive multiple lamps, then even with LEDs they are then adding more load than a single LED would and preventing flicker because of that additional load. So we'll go with that for now
Not to throw a monkey wrench into this, but I put 4 LEDs in one of my Sterns (no Aux lamp driver) and they behave like incandescents until a certain number of playfield lights are lit, like 20 or so, then they begin to flicker and get worse as more bulbs are lit.