Takes the guess work out of connecting trailers. Tests tail light, stop/turn lights, and ground. Plugs into the connector of the tow vehicle. Easy to see bright LEDs LED's typically have a lifespan of 10+ years. ⚠ WARNING: This product can expose you to Lead, DBP,CD, BPA ,hexavalent chromium, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.