Boss Part # MSC09471 - 13-Pin Headlight Adapter Kit Negative Switch SL3 Relay Kit 99-02 GM. This is only used on Boss plow wiring setups which have the 13-pin wiring harness. This headlight adapter is used on the 1999-2002 GM trucks which have the SL3 lights on the plow. The SL3 lights are the LED newest style of plow lights found on all Boss plows. This harness adapter will plug directly into your 1999-2002 GM truck lights and allow your truck lights to flip to your plow lights when you snowplow is hooked up.