1973–1987 Chevrolet & GMC Truck Wiring Harnesses
1973–1987 Chevrolet & GMC Truck Wiring Harnesses (Squarebody)
Bring your Squarebody back to life with modern reliability. The Painless 27-Circuit Classic-Plus Wiring Harness (P/N 20205) is built for 1973–1987 Chevy and GMC pickups, as well as Blazer and Suburban models through 1991.
This harness features a factory-style bulkhead connector that mounts directly to the stock firewall location—no cutting, trimming, or drilling required. With pre-terminated connectors, dual fuel tank support, and extra-long headlight and taillight wiring, this is the most complete and adaptable Squarebody wiring system available.
Each wire is GM color-coded and printed every 12 inches, simplifying installation and future maintenance. Whether you’re restoring a C10 or wiring a fully custom LS-swapped K10, Painless makes it easy to wire your truck once—and wire it right.
Why Choose Painless for Your Squarebody Build
Designed for ’73–’87 Chevy & GMC pickups, Blazers, and Suburbans
Bulkhead-mounted fuse block fits stock firewall location
Dual fuel tank support included
Extra-long light wiring for any bed or body configuration
GM color-coded, labeled wires for clean, simple installation
MIDI fuse protection eliminates failure-prone fusible links
Built in the USA with lifetime warranty and tech support
27-Circuit Classic-Plus Customizable GM Truck Chassis Harness (P/N 20205)
The Painless 27-Circuit Classic-Plus Harness provides all the circuits your 1973–1987 Chevy or GMC truck needs—and then some. Designed with modern performance in mind, this kit supports electric fuel pumps, high-output alternators, power accessories, and dual fuel tanks while keeping a clean, factory-style installation.
Every major connector comes pre-installed, including ignition, dimmer, blower, and wiper circuits. For the few open-ended connections, heat-shrink mastic terminals are included to ensure waterproof, professional-grade connections.
Key Features:
27 total circuits / 18 fuses with horn relay and MIDI fuse
Factory-style bulkhead connector—mounts in stock location
Pre-terminated connectors for ignition, dimmer, blower, and cluster circuits
GM color-coded and labeled wiring for easy routing and service
Dual fuel tank ready—secondary harness included
High-amperage charge wire with MIDI fuse (no fusible links)
Extra-long front and rear lighting leads for different bed and front-end configurations
Compatible with C10, C20, C30, Blazer, and Suburban
Includes Circuits For:
A/C & Heat, Accessory/Camper Light, 4WD Switch, Backup Lights, Brake Lights, Charging, Cruise Control, Dome Lights, Electric Choke, Electric Fuel Pump, Fan Relay Power, Fused Power Source, Headlights, Horn (Relay), Ignition Coil, Instrument Lighting & Gauges* (Brake Warning, 4WD, Fuel, Oil, Tach, Temperature, Speakers), Park Lights, Power Door Locks, Power Windows, Radio/Clock (Constant & Switched), Starting, Tail & Third Brake Lights, Turn Signals, and Wipers.
Compatible Socket Pigtail Kits:
30350 – Single Round Headlights (’73–’80)
30351 – Single Square Headlights (’80–’87)
30352 – Dual Square Headlights (’80–’87)
30353 – Suburban Dual Square Headlights (’88–’91)
Perfect For:
Builders wiring a 1973–1987 Chevy/GMC Squarebody truck, Blazer, or Suburban who want a plug-in, professional-grade solution with support for power accessories, dual tanks, and modern charging systems. Ideal for carbureted and standalone EFI setups alike.