Pulse ignition wiring

Question

I took the front panel off of the unit and the pulse ignitor has 4 wires coming out of it. 3 wires are the same and are hooked up to the 3 different ceramic sparkers( don't know the name ) and then ther's a 4th wire which is skinier and about 6-7 inches long. The question--where the heck does the 4 wire get connected to, I don't see anything that looks like it should be connected to it