Breakaway Kit : A kit designed to apply power to the trailer's electrical brakes in the event that the trailer becomes disconnected from the hitch while on the road. Required in most States and Provinces. Comes with a charging battery to maintain power if the breakaway occurs.

Circuit Breaker : A switch that automatically interrupts the current of an overloaded electric circuit.

Flasher : A device for automatically flashing a light (ie. Hazard lights on a vehicle)

Fuse : An electrical safety device consisting of or including a wire or strip of fusible metal that melts and interrupts the circuit when the current exceeds a particular amperage.

Relay : An electromagnetic device for remote or automatic control that is actuated by variation in conditions of an electric circuit that operates in turn other devices (as switches) in the same or a different circuit.

Solenoid : Mechanically parallel the main battery to the auxilary battery providing mechanical separation of the batteries.

Testers : Designed to allow testing of wiring installations / deficiencies on vehicles and trailers. Test turn signals, brake lights & ground wiring to find any short circuits in the wiring. 

Trailer Lights: There are a number of brands of trailer light manufacturers. By law, a trailer must have brake / turn signals / running lights and marker lights.