25 Circuit Harness - Pro Series Truck GM Key

The 25 Circuit Harness - Pro Series Truck GM Key from Painless Wiring is a complete, customizable electrical solution designed for serious truck builders and restorers working with GM platforms. This harness eliminates the complexity of factory wiring by consolidating 25 individual circuits into an organized, modular system that accepts column-mounted ignition switches. Whether you're performing a frame-off restoration, converting to modern engine management, or simplifying an aging electrical architecture, this harness provides the foundation for a reliable, code-free installation that bypasses problematic original wiring.

The Pro Series design incorporates a bulkhead firewall pass-through configuration, which isolates engine bay circuits from cab wiring and reduces voltage drop across long wire runs—a critical feature for trucks running high-demand fuel injectors, electric fans, or aftermarket ignition systems. The 25-circuit architecture provides sufficient capacity for fuel injection, ignition, charging system, lighting, cooling fans, and auxiliary accessories without daisy-chaining components or risking thermal overload. Color-coded wiring and clearly labeled connectors follow industry standards, making troubleshooting and future modifications straightforward. The harness kit includes all necessary terminals, relay bases, and connectors; at 15.75 pounds with compact 10.4 x 6.8 x 15.5 inch packaging, it ships efficiently without sacrificing build quality or conductor gauge integrity.

Mechanics and fabricators restoring Chevrolet, GMC, or Oldsmobile trucks from the 1960s through 1990s will find this harness particularly suited to restorations where factory harnesses are brittle, unavailable, or incompatible with modern engine swaps. The in-column key configuration integrates seamlessly with period-correct or reproduction steering columns, and the modular design allows installers to populate only the circuits required for their specific application—reducing clutter and cost. Professional installers appreciate the Painless Wiring reputation for technical support and the ability to cross-reference wiring diagrams by circuit function rather than hunting through factory schematics. This harness is the preferred choice for quality restorations where reliability and electrical safety are non-negotiable.