Smart Glow fuses are innovative automotive style fuses (ATO, Mini, Maxi and glass tube) that feature an indicator light that glows when the fuse is blown, saving time to troubleshoot an open circuit * The ATO Fuse was designed and patented by Littelfuse in 1976 and set the standard for automotive circuit protection * It features industry standard color coding to indicate amperage rating, 20 amp is yellow * Snaps into place without the use of tools