Painless Wiring For Classic Cars
About this episode
Dennis Overholster from Painless Performance Products breaks down how classic-car wiring harnesses get reverse-engineered and built, from sourcing wire and choosing gauges to the documentation and customer support that follow. He also explains how Painless designs universal harnesses by asking where the fuse block mounts and whether the car has power windows and door locks, including why they often include extra-long wire lengths. The conversation ties it together with the “painless wiring” origin story and the brand’s long development timeline.
Wiring is where a lot of classic car projects go to die: brittle insulation, mystery splices, random colors, and “temporary” fixes that turn into permanent hazards. From the Lone Star Street Rod Association State Run in Granbury, Texas, we sit down with Dennis Overholster from Painless Performance Products, the company so many builders mention when they want a clean, reliable automotive wiring harness for a street rod, classic truck, or restoration.
Dennis breaks down what Painless actually does day to day, from using tens of millions of feet of wire each year to building harnesses by hand on layout boards for consistent routing and branch lengths. We get into the real craft of reverse engineering: bringing a vehicle into the shop, deconstructing the original harness, building prototypes, test-fitting, documenting every change, and then producing a kit that’s repeatable. If you’ve ever wondered why a good harness costs what it costs, the “it can take a year to get it right” explanation lands hard.
We also go practical with classic car electrical upgrades: six volt versus twelve volt systems, choosing wire gauge with headroom, and why a simple relay often fixes problems when modern accessories like air conditioning demand more current than the original circuit can safely deliver. And if you’re nervous about installation, you’ll love hearing about the full-color manuals and the phone support that helps first-timers avoid expensive mistakes.
If you enjoy smart car talk and want fewer electrical surprises, subscribe, share this with a friend who hates wiring, and leave us a review so more builders can find the show.
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1955 Chevy Corvette
"And somehow, someway I guess you went backwards with a wiring harness for that truck or you know, my 1955 Chevy Corvette. You went backwards, you took the wiring harness out of it, said, Oh, okay, so this is the way we're gonna do it."
This is a 1955 Corvette made by Chevrolet. The speaker is talking about the car’s wiring system—basically the bundle of wires that powers lights, gauges, and other electronics—and how they replaced it while working on the car.
A 1955 Chevrolet Corvette is an early-generation Corvette where classic wiring and electrical systems are a big part of restoration work. In this segment, the host talks about pulling and replacing the wiring harness on the 1955 Corvette, which is common when the original wiring is damaged, missing, or unsafe.
wiring harness
"And somehow, someway I guess you went backwards with a wiring harness for that truck or you know, my 1955 Chevy Corvette. ... And I got a brand new wiring harness. ... what is the latest and newest wiring harness that you have on the market today that we can buy?"
A wiring harness is the car’s main set of wires, usually bundled together, that connects everything electrical. If it’s old or damaged, it can cause problems like dead lights, weird gauges, or even electrical shorts, so people replace it during restoration.
A wiring harness is the factory-style bundle of wires and connectors that routes power and signals to the car’s electrical components. Classic-car restorations often involve replacing or reworking the wiring harness because old wiring can be brittle, corroded, or modified in unsafe ways.
reverseengineer
"And uh I got a brand new wiring harness. Yeah, you uh had to reverseengineer it. And uh we made so what possesdy outodothis?"
Reverse engineering means you learn how something is built by looking at what’s already there. In car wiring, it can mean tracing wires and figuring out which wire does what so you can rebuild it correctly.
Reverse engineering means figuring out how something works by studying it—often by taking it apart, tracing connections, and mapping functions. In wiring work, that can mean analyzing an existing harness or diagram to recreate the correct wiring layout when documentation is missing.
electronics school
"I went through electronics school in the military, and then after I got out, I went uht took two years of DeVry electronics school, and I've just always done it. So you're an electronics engineer."
Electronics school is training in how electrical systems work. That kind of knowledge helps when you’re fixing a car’s wiring because you need to understand circuits and how to find what’s wrong.
Electronics school refers to formal training in electrical circuits and troubleshooting methods. For classic car wiring, that background helps with diagnosing faults, understanding how components interact, and building or repairing harnesses safely.
El Camino harnesses
"Well,see,wewejustintroduceduhthreenewElCaminoharnessesfortheuh68through72."
An El Camino is a classic Chevrolet that’s part car and part pickup. This segment is about making replacement wiring harnesses for the 1968–1972 model years, so you can add or update things without hacking the original wiring.
The Chevrolet El Camino is a classic American car that combines a passenger car body with a pickup-style bed, and it’s popular for retrofits like wiring upgrades. In this segment, the hosts specifically discuss new wiring harnesses for the 1968–1972 El Camino, which matters because older cars often need correct circuits and connector layouts to make modern accessories work safely.
square box
"Sothenextquestionisstillapopularsquarebox. Ohyeah."
They’re referring to a common “box” style electrical setup used in older cars. The shape and layout matter because it determines how the wires connect and how the system is organized.
“Square box” here refers to a common classic-car wiring/harness form factor—typically a rectangular, box-style electrical module or junction area. For wiring work, the physical layout matters because it affects how circuits are routed, terminated, and protected.
twelve-volts systems
"Sothethenextquestionisdoyoudosixvoltsandandtwelvevoltsystems? Yes."
A 12-volt system is the standard electrical setup in most cars. They’re comparing it to 6 volts because the wiring and power needs can be different.
A twelve-volt system is the modern standard for most vehicles, with the battery/charging system operating at 12 volts. The hosts are comparing 6-volt vs 12-volt setups because circuit requirements (like current draw) can change how you design or select wiring and protection.
10ampsto operate it correctly
"Butwhatwhatwedoisifthethecircuitrequiresuh10ampstooperateitcorrectly,uhwe'regonnaandthenitandittakesauhuh16gaugewiretodothat."
“10 amps” is how much electrical current the circuit needs. If the current is higher, you need thicker wiring so it can safely carry the load without getting hot or losing power.
“10 amps” refers to the current the circuit needs to run correctly. When current is higher, the wiring must be thick enough (lower gauge number) to avoid excessive voltage drop and overheating, so harness designers choose wire gauge based on amperage.
16 gauge wire
"Butwhatwhatwedoisifthethecircuitrequiresuh10ampstooperateitcorrectly,uhwe'regonnaandthenitandittakesauhuh16gaugewiretodothat."
Wire gauge is basically how thick the wire is. Thicker wire can handle more current safely, which is why they’re talking about 16-gauge versus 14-gauge for the circuit.
Wire gauge is a measurement of conductor thickness, and it strongly affects how much current a wire can safely carry. In this segment, they say 16-gauge wire is what’s needed for the circuit’s 10-amp requirement, then they discuss making it 14-gauge for their harnesses.
14gauge
"We'regonnamakeita14gauge."
14-gauge wire is thicker than 16-gauge. Thicker wire can handle more electricity more safely, so it helps the circuit run correctly.
14-gauge wire is thicker than 16-gauge, meaning it can carry more current with less voltage drop and less heat. The hosts explain they “make it 14 gauge” to support the circuit’s needs and to give the customer flexibility for adding accessories.
resistance
"Thatwaythecustomercanaddaradiolessresistance,yeah,right. Anditcouldberunningonasix-voltsystemaswell."
Resistance is how much a wire or connection slows down electricity. In wiring, lower resistance usually means less power loss and better performance for the circuit.
Resistance is the opposition to electrical current flow, measured in ohms. The hosts mention “less resistance” in the context of wiring/accessory additions, which matters because lower resistance can reduce voltage drop and help the circuit deliver the needed current.
six-volts system
"Anditcouldberunningonasix-voltsystemaswell."
Some classic cars use a 6-volt electrical system instead of 12 volts. Because it’s lower voltage, the wiring often has to be sized differently to deliver enough power.
A six-volt system is an older vehicle electrical standard where the battery and charging system operate at 6 volts instead of the modern 12 volts. That difference changes how much current a circuit draws for the same load, which directly affects wiring gauge and fuse/relay sizing.
relay
"well,wejustneedtoaddarelaytothisparticularsystem,andhere'showyouactivateit,andyouactivate it with the wire thatyouweregoingtouse."
A relay is like an electrically controlled switch. It lets a small control signal turn on a bigger power circuit, which helps protect the wiring and makes accessories work more reliably.
A relay is an electrically controlled switch used to let a low-current signal control a higher-current circuit. The hosts recommend adding a relay to the air-conditioning system so the wiring can handle the load reliably without over-stressing the original wiring.
direct battery voltage
"Sonowwegetdirectbatteryvoltagethroughtheairconditioner,andtheoriginalwirejustlikethat."
“Direct battery voltage” means the accessory gets power straight from the battery. That helps it receive enough power to work correctly, especially when the original wiring isn’t designed for modern loads.
“Direct battery voltage” means powering a component straight from the battery (often through a fuse/relay), rather than through thinner or shared factory wiring. This reduces voltage drop and helps ensure the accessory—here, the air conditioner—gets the voltage it needs to operate properly.
color code
"Doyouusethesamecolorsasthefactory? ... Whywouldn'tyouuseitlikethat? ... There'sathere'safew,youknow,GeneralMotorshasgotthethemostbasiccolorcodeandthey'vebeenusingitforyearsandyearsandyears."
Car wiring uses different colored wires so you can tell what each one is for. When people restore a classic car, they try to match the original wire colors so it’s easier to work on later.
A color code is the standardized wire color scheme used by automakers to identify what each wire does in the factory wiring harness. Classic-car restorations often try to match these colors so troubleshooting and future repairs are easier and more correct.
work order
"Andthenweputitinthecomputertomakeaworkorder. Andthenwegetwhenwegetallthatdone,we'llrunaworkorderforthree,andwe'llseeifitseeifit'sseeifyoucanproduceit."
A work order is a written checklist that tells the shop what to make and what steps to follow. It helps the process stay organized and repeatable.
A work order is an internal instruction sheet that tells a shop what to build or produce and how to do it. In wiring-harness fabrication, work orders help standardize the steps and ensure the harness can be reproduced consistently for multiple cars.
taillight wires
"Sowemadeit16feetlongforthetaillightwires. [906.6s] Well,cometofindout,thatwasn'tlongenough. [909.2s] Sowewent22feetlong."
These are the wires that power the rear tail lights. When you’re rewiring a classic car, you have to make sure the wires are long enough to reach where the lights mount.
“Taillight wires” are the vehicle wiring runs that feed the rear lighting (tail lamps) from the car’s electrical system to the rear lamp assemblies. In classic-car wiring work, the key challenge is routing and length so the harness reaches the mounting points without strain.
headlight wires
"Andthealltheheadlightwiresandsoforthareall16feetlong. [915.9s] Sothecustomer'sgonnagetit,they'regonnagetalotmorewirethantheyneed,butthat'sgood. [921.6s] It'seasiertoshortenitthanitistolengthenit."
These are the wires that power the front headlights. The point is to have enough wire length so the lights can be mounted and connected properly.
“Headlight wires” are the wiring runs that supply power to the front headlamp assemblies. The discussion here is about building a harness with enough length for unknown routing and mounting locations on different classic cars.
shorten it than it is to lengthen it
"Sothecustomer'sgonnagetit,they'regonnagetalotmorewirethantheyneed,butthat'sgood. [921.6s] It'seasiertoshortenitthanitistolengthenit. [924.2s] Now,doyouputtheconnectorsontheends?"
This is a practical wiring-harness rule: it’s generally easier to shorten an overlong wire run than to extend one cleanly later. Extending usually means adding more splices/connectors, which can introduce extra failure points and messy routing.
connectors
"Now,doyouputtheconnectorsontheends? [926.5s] Onlyincertaincircumstances. [928.6s] Ifthey'regonnahaveuhageneralmotorkeyscolour,let'ssaykeycollar,thenwe'llwe'llputalltheplugsonthatsotheycanjustpluginthecollar."
Connectors are the plug-together ends on the wires. They help you attach the wiring to the car’s lights without hardwiring everything.
In wiring harnesses, “connectors” are the plug-in interfaces at the ends of wires that let you join the harness to the car’s lights or switches. The host explains they only pre-install connectors in certain cases so the customer can plug the harness into the correct color-coded leads.
general motors key's colour
"Ifthey'regonnahaveuhageneralmotorkeyscolour,let'ssaykeycollar,thenwe'llwe'llputalltheplugsonthatsotheycanjustpluginthecollar. [938.0s] Done. [945.4s] Butlikeyousay,howlongdoyouneedtogetyourtaillights?"
This is about wire/connector color-coding. If your car uses the GM color scheme, the harness can be set up so the plugs match the right connections.
“General Motors key’s colour” appears to refer to GM’s color-coding conventions used to identify specific circuits or connector types in harnesses. The idea is that if the customer’s car uses that GM color scheme, the harness can be pre-terminated so the plugs match correctly.
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