HP Smart Coil ignition sub-harness. Includes a pair of coil harnesses for an 8 cylinder engine. These harnesses are similar in design to factory GM LSx coil harnesses, but plug into Holley HP Smart Coils. They plug into Holley LSx plug and play main harnesses if one wants to replace factory LSx coils with Holley HP Smart Coils. If using a non-LSx main harness, purchase PN 558-307 for connectors, wiring, terminals to connect directly to a Holley HP or Dominator ECU