HDE-1 dual fire ignition by Compufire. All circuits are contained on the timing plate. The HDE-1 has fixed advance curves and 6500 RPM rev-limiters to protect the engine. Has accu-Ray timing LED for precise timing and system check. Fits Big Twin Shovelhead & Evo models with carburetor 1970 - 1999, and Ironhead / Sportster 1971 - 2003 (Will not fit models with EFI, Twin Cam, or 1200S).