Bigmig the relay plugs into your smoker wires. so when you start up the tank you get the henlnog start up sound. when the henlong engine sound fires up the smoker wires get power and that turns on the thunder system. which is really neat because when the thunder module kicks in it revs up just for a second. as best as i can understand the system one 9.6 battery powers the electronics and also powers the amp. and the other 9.6 battery provides even more power for the amp. the instructions made hook up easy..... it has a spouse warning