On system 11 games (or older) you may find that when using LED flashers, the flasher stays lit when it should not be. This is caused by the warming resistor in the flasher circuit. It stores up some voltage so that the incandescent flasher, which is much slower to light and fade than an led, has some voltage to have less of a voltage ramp. The solution here for LED flashers is to remove this resistor so that the voltage is not stored. There are actually a couple options to get your LED flashers to work in one of these games:
1) If the flasher has a backbox counterpart, you can leave the backbox flasher incandescent and use an LED flasher for the playfield. As long as the backbox flasher is not burnt out, this should drain away the ramp up voltage in the circuit. Since we usually don't recommend backbox flashers anyway, this may be your solution. In this case, no game modifications are needed.
2) Remove either the ground wires to the led flasher resistor board, or cut one of the legs off of the smaller resistor on the board. There are usually 4 resistors per board.
You will want to clip only one leg on each of the 2 small 330 ohm resistors leaving the large resistors alone. These aren't really needed and Williams started leaving them out of the circuit on games starting with Big Game anyways.
On some older games the resistors may look a little different. Here is a photo out of a system 3 flash:
Here is gorgar warming resistor:
Here is a Firepower warming resistor:
