This external plug-in ignition module offers ease. Just remove the OEM ignition module, and replace it with the low profile billet aluminum Twin Tec module. This gives you four rotary switches to select either Single- or Dual Fire application, two advance curve families with adjustable advance slope to accommodate for stock to highly modified engines, adjust timing advance, and set the RPM limit in 100 RPM steps. Two diagnostic LEDs indicate general status and the status of the vacuum (VOES) switch. When used for static timing the status LED will flash when the engine reaches Top Dead Center (TDC). Works in Dual Fire mode with the stock 3 Ohm coil. When you want to use the module in Single Fire mode you have to order matching Single Fire coils separately.