Battery pack for lanyard breakaway system

If your talking about the small black box the cable comes from for your breakaway,the small black box is just a switch,the 2 wires going in and out of the back,one wire goes to battery,the other goes to your electric braking system on the trailer, when the cable coming out the front is connected to your hitch,it is for safety, if you trailer should come unhitch,that cable will pull out the "plunger" once its pulled out ,the switch will be activated, completing the circuit, sending 12 volts to your brakes from your battery,stopping the trailer from rolling down the highway on its own. You can test it by pulling out the plunger by the cable,just give it a jerk,once its out, you brakes will be on ,on the trailer,provided your battery is charged, the plunger can be snapped back in.