GE Speedtronic Mark IV DS3800NSFC1J is a System Firing Board and it's a part of the Mark IV Series. It's built to take a small auxiliary card (DS3800DSFC) that allows the motherboard access to an additional potentiometer when attached. The auxiliary connects by two board-to-board pins and is secured in place. Four nylon pins already affixed to the DS3800NSFC1J surface sustain it. One light-emitting diode, branded "IMOK," is included in the DS3800NSFC1J. This LED is amber in color.