The part number is 273-0079, and was $5.49. The factory security module has a plug to allow connection to the HD siren. I just tinned the two leads from the siren, and inserted them into the first two slots shown on the plug in the photo. Then I taped it up with electrical tape to see if it worked. It chirps when you turn off the main power switch to the bike (at the same time the lights flash to indicate the system is armed). It also then starts chirping a warning when the bike is moved (sounds a few times and then goes off full tilt). Red wire from siren goes to the brown wire on the Harley plug, and the black wire from the siren goes to the green wire on the plug. I just used a soldering iron to tin the siren leads to give them body to insert into the Harley plug. The Harley plug has 2 rows of pins, use the rows that do not have the metal visible when you are looking at the plug... look at it and you will see what I'm talking about. One row is connected to the wires on the back of the plug and the other is not. Once you get the wires inserted I then wrapped some electrical tape around the plug to keep the wires in place and re-inserted the plug back into the female receptacle on the chassis molding where it was originally stored. I drilled out the mounting holes on the siren to accommodate a wire tie(plastic zip tie) and secured it place where the OEM siren would go. It chirps to warn you a couple of times and then goes off for about 20 seconds, then resets itself.