Wiring Harnesses

What Types of Wiring Harnesses Can You Buy for a Classic Car?

You can buy complete chassis kits, engine swap harnesses, dash harnesses, ignition sub-harnesses, fan kits and accessory harnesses. The right one depends on whether you're rewiring the whole car or fixing one system.

This category sits within wiring, relays & switches, part of our larger lineup of ignition, electrical & tuning parts. Here's what each harness type covers:

• Complete chassis harness kits that rewire lights, gauges, ignition and accessories across the whole car
• Engine swap harnesses that connect a late-model engine and transmission to an older chassis
• Dash and gauge harnesses, such as a 10-circuit universal dash wiring harness
• Ignition and distributor sub-harnesses, including HEI 4-pin harnesses for GM and 3-wire distributor harnesses
• Electric fan harness kits, including kits with a 185-degree thermo-switch
• Lighting and accessory harnesses, such as an American Autowire passenger-side front light harness or a convertible top harness

If your original wiring is brittle or heavily spliced, a complete kit is the cleaner fix. For a single failed circuit, a sub-harness saves you time.

How Many Circuits Does Your Classic Auto Wiring Need?

Most street-driven classics need a 21-circuit harness, while race-only cars can run 10 circuits. If you're adding A/C, power windows, EFI or electric fans, step up to a 23- or 25-circuit kit.

A 10-circuit harness suits cars that don't need street-legal lighting and accessory circuits. Painless Performance Products offers a 10-Circuit Race-Only Wire Harness built for that job.

A 21-circuit wiring harness covers the lighting, signals, horn, wipers and gauges a street car needs. Painless offers a 21-Circuit Pro Street Wire Harness for street-legal race cars. There's also a 21-Circuit Color-Coded Wire Harness for 1966-1976 Ford Galaxie, LTD, Falcon, Fairlane, Maverick, Torino and Ranchero models.

Before you order, check our 21-circuit wiring harness diagram guide to see how each circuit is laid out.

Painless Pro-Series 23-Circuit and 25-Circuit kits add circuits for extra accessories. Both come in GM keyed column and key-in-dash versions. Count every accessory you plan to run, then leave room for future upgrades.

Universal Wiring Harness vs. Vehicle-Specific Harness

Choose a vehicle-specific harness if you want factory-style routing and faster fitment. Choose a universal wiring harness if your build is heavily modified or has no factory equivalent.

A vehicle-specific harness is made for a particular chassis, so it's quicker to install and easier to troubleshoot later. The Ford 21-circuit harness above is one example.

A universal harness gives you extra wire length and color-coded, labeled circuits that you trim and terminate yourself. That flexibility makes it a common hot rod wiring harness choice for street rods, custom dash layouts and builds with relocated components.

Universal kits take more planning. You'll route each circuit, cut it to length and crimp new ends, so stock up on wiring terminals & components before you start. Our wiring harness installation guide walks you through the process step by step.

Whichever type you pick, confirm your column style, gauge setup and accessory list first. Those details decide which kit fits your car.

What Do You Need in an LS Swap Wiring Harness?

You need an LS swap wiring harness that matches your engine generation, throttle type and transmission. Miss any one of those, and you'll face connectors that won't plug in or an engine that won't run right.

JEGS engine swap wiring harnesses cover several common combinations:

• 1997-2004 GM 5.7L LS1 & LS6 and 1999-2006 GM Vortec 4.8L-6.0L V8 engines with a GM T-56 transmission
• 2009-2014 GM Gen IV LS3 6.2L & L92 6.2L truck engines with a 4L80E transmission and drive-by-wire throttle
• LS3 & L92 engines with a T56 or TR6060 manual transmission and drive-by-wire throttle

Check whether your engine uses drive-by-wire or a cable throttle, and whether you're running an automatic or a manual. The engine swap wiring harness handles the engine, but you'll still need to plan power, ground and fuel pump feeds from your chassis harness.

For the full process, read our guide on how to do an LS engine swap.

What Parts Complete an Automotive Wiring Harness Install?

A complete automotive wiring harness install also needs connectors, fuse protection, relays and wire covering. Order these parts with your harness so the job doesn't stall halfway through.

Round out your order with these parts:

• Electrical connectors for joining harness sections to lights, gauges and sensors
• Fuse panels for adding protected circuits beyond what your main harness provides
• Relays for high-draw loads such as electric fans, fuel pumps and headlights
• Wire covering & protection, such as JEGS convoluted tubing in 1/4" x 15' lengths
• Surge protection, such as the Painless Electrical System Surge Protector that regulates spikes at 14.5 volts

Grounds matter as much as feeds, so plan clean ground points for the engine, body and dash. Once everything's in hand, lay the harness out in the car before you make any connections. Test each circuit as you go, and you'll catch problems while they're still easy to fix.