Some of the Dyna FS ignitions have a rpm output that is designed to drive small loads such as relays and LED lamps. It is designed to turn on at certain RPM ranges that you can program using the programming software. It is a low side driver meaning that you connect one side of the load(relay, 12V lamp, etc) to 12V, and the other side of this load to the Dyna FS output wire. The signal wire for this is a wire with a bullet style connector on it. On most Dyna FS ignitions, it is a blue wire, or a brown wire. But consult your ignition instruction sheet to determine exactly which wire it is. The output is capable of driving up to 500mA of current, so make sure that you use a relay to drive higher current loads.