Description The Trailer Isolation Relay Package is required for all applications. This harness safely & properly applies the load from the trailer lighting to the battery & not to the rest of the bike’s wiring/relays/fuses. Subharness assemblies are required to complete the installation & are sold separately. Specific subharnesses are available for GL1800 & GL1500 models and a universal subharness is offered for other motorcycles. The 4-wire Trailer Converter is required to connect the 5-wire Trailer Isolation Relay Package to trailers with only 4 wires.