The Siren comes with all the necessary harnesses to install it. You will need 14 gauge wire to run to your power source and for your ground wire. The speaker uses 16 gauge wire to run from it to the harness. You can get this wire from us or you can usually source is locally from a NAPA or auto parts store. You can find the full install guide here http://www.whelen.com/install/140/14045.pdf. Hope this helps. If you have any other questions let us know.