That sounds like a switch that doesn't have quite enough of a gap when it's open and gets vibrated closed. Have a schematic?

Read the 10th post down:

http://pinside.com/pinball/forum/topic/ems-and-leds

It is possible that a "Better" LED might solve your issue. If they have such, an LED with a smoothing cap built in might prevent the LED from lighting with such a small fast pusle of power.

Buy non ghosting LEDs from Cointaker and your problem will go away. They're not cheap, but they'll last forever and it's worth the money if you want to go this route.

Sometimes regular LEDs will ghost in some places, and and sometimes they won't. But these won't, in any place.

See also:

http://pinside.com/pinball/forum/topic/how-to-troubleshoot-lightbulbs-being-backfed-williams-blue-chip

I was experimenting with some LED's just a week ago on my SC, mind sharing a couple pics of what's working out for you. What type of LED's are you using? Mine don't seem bright enough to make a difference.

After reading all these responses, I might be full of crap about the switch closures. I don't have any direct experience using LEDs in EMs, and didn't even consider that crosstalk from coils might be enough to light LEDs! You should listen to these other guys.

I like Cointaker, they have treated me right, but they are not the only ones now with non-ghosting bulbs-that is what you want. There is a certain amount of stray voltage that can bleed thru the system with EMs (probably solid state too, but may be dealt with blocking diodes). Incandescent bulbs are not as sensitive to this and don't really light unless there is close to full load-or so I have been told by the pinball gurus.

I don't doubt that others have them. I just have had good experiences with them, so I stick with them.

I had one that ghosted and I called them. Chris replaced it no charge.