Advice, Encouragement, and Products to Help With Your Next Hot Rod Electrical System Project

Wiring can be intimidating. If you nodded when you read that, you’re not alone. Wiring a vehicle, or even installing an electrically controlled accessory, can indeed be a challenge. But if you step back, read the instructions, and prepare yourself with the right tools, you might find the act of connecting, routing, and finishing a wiring project to be straightforward and rewarding.

Getting into the nitty-gritty and theory of electronics will likely short circuit your head, but that’s what the engineers handle on a daily basis at the top wiring companies in the hot rod world. They work hard to design and produce the accessories, harnesses, and controls to make it easy for most hot rodders to use and install simply by taking our time, planning ahead, and using the right tools for the right jobs. One more thing – READ THE INSTRUCTIONS!

In reaching out to a number of wiring companies for their input on wiring and vehicle electronics, the number one action suggested was to look at the instructions before installing the parts. Many companies put a lot of effort and time into their installation guides and dollars to doughnuts that somewhere in those pages is the answer to your question.

No matter where you sit in electronics and wiring experience, there are some great solutions and components available to help with pretty much anything you can dream up. One thing for sure is that we’re putting more electronics in these old cars than their electrical systems were ever designed for. If you plan to install an EFI system, adjustable air suspension, or even a set of dual electric fans, it’s a good idea to run new wiring or an auxiliary distribution block unless you’re installing a completely new vehicle harness.

We spoke with a number of companies that manufacture complete wiring harnesses, but when you visit their booth at a show or dig through their website, you’ll be surprised at the number of accessories and wiring solutions they offer, from bulk wire to crimp tools, LED lighting to fuel pump relay harnesses. They’ve done the heavy lifting to ease the process for you!

Most wiring takes planning and patience. By doing the job right the first time, you’ll have miles and miles of worry and trouble-free cruising ahead of you.

wiring an old car, wiring old truck, msd relayMSD Performance

Righteous Relays

Relays play an important role in wiring your vehicle properly, as they’re a means to supplying high current through the use of a low-current switch. The most common use is to supply the high current to an electric fan or fuel pump, or even a horn. MSD has taken the standard relay operation to the next level with their Solid State Relay to ease wiring and keep things clean under the hood or behind the dash.

The MSD Solid State Relay has four 35-amp channels that can be used separately or wired together. Each channel can be triggered by a switched power or ground source for a combined output of 140-amps. In the case of a short or overload, this smart relay simply disables the circuit temporarily and resets with the next key cycle. The Solid State Relay is helpful when installing EFI to help isolate the ECU and sensors to minimize electrical interference. Available in red or black.

wiring an old car, wiring old truck, fuse and relay blockCE Auto Electric Supplies

Distributing Voltage

As electrical accessories are added to your hot rod, nearly every manufacturer tells you to connect the power source directly to the battery terminals. Not only is this unsightly for a well-built car, but it can also cause interference issues, poor connections, and other hazards. The solution is to install a small power distribution center. The sample shown measures only 6.5x 2.5-inchs and simply connects to the battery terminal to safely feed several circuits.

CE Auto Electric Supply offers a number of distribution block kits for you to assemble or can provide a custom-built, ready-to-go system for your application. Each system is easy to install and cleans up the wiring, but more importantly, it provides a much more effective and safer way to run each electrical system through fused circuits while isolating the voltage supply to reduce the chance of electrical interference and intermittent gremlins.

Tech Tip #1

wiring an old car, wiring old truck, up flasher

If you’ve ever updated to LED brake lights or running lights, you may have run into the issue of the turn signals flashing too fast or inconsistently. This is because the LEDs have such low load resistance compared to the original bulbs that the flasher can’t control them. The solution is simply to replace the original-style flasher with an updated LED-friendly flasher such as this model from United Pacific. It simply plugs in place and has a small ground wire to connect.

wiring an old car, wiring old truck, united pacific squarebody lightsUnited Pacific

LED for Squarebodies

There’s a reason everyone is talking about Light Emitting Diodes for lighting upgrades in their garage, home, and hot rods. LEDs are brighter and use a fraction of the current compared to their incandescent counterparts. In many cases, there are replacement LED ‘bulbs’ that simply plug in place of the original 1157-style socket, but United Pacific offers a number of complete LED parking light assemblies, with their latest for ’73 –’80 C10s.wiring an old car, wiring old truck, up car parts, united pacific lights

These new parking light fixtures feature 17 bright amber LEDs housed in a complete assembly with a clear or amber lens. The electronics are fully sealed in epoxy to resist corrosion and are highlighted with a stainless steel trim ring. The lights function as both parking lights and bright turn signals so people will easily see you coming and where you’re going. Better yet is that the assembly is a direct bolt-in and connects by plugging it into the existing 1157-style socket.

wiring an old car, wiring old truck, snap on wiring pliersSnap-On

Strip and Crimp

Adding more electronics and controls to your project means working with a lot more wiring, which means you need the right tools to complete the job. One of the tools you’ll need is a good set of wire strippers and Snap-on can set you up.

These USA-made Stripper/Cutter/Crimpers will produce a firm crimp and reliable strip every time. The spring-action motion increases the leverage and reduces fatigue, while the compact overall size makes working in tight confines easier. The knife-type blades provide clean, accurate stripping and will take off up to 7/8-inch of the wire sleeve. Snap-on offers a number of different sizes for specific wire gauges and terminal crimps to suit any wiring task.

Tech Tip #2

wiring an old car, wiring old truck, wire crimp

When crimping wires and terminals, it’s important to ensure you have the right tool and understand the crimp process as there are a number of different terminals available. Painless Performance shared these pics of a common OEM-style terminal that has two sets of crimp tabs; one to grasp the insulation of the wire, and the other to crimp onto the bare wire. A proper set of crimpers are also required, depending on the terminals being used.

wiring an old car, wiring old truck, american autowireAmerican Autowire

Prepare for Connections

Getting ready to start a wiring project or perhaps have some smaller scale electrical repairs coming up? Installing components with locking, sealed connectors will give you peace of mind and American Autowire can help you be prepared with their Professional Weather Pack Terminal & Connector Kit.

This 429-piece kit is supplied in a durable storage container filled with all of the terminals, seals, and connectors you’ll need to do the job right the first time. There are connectors for 1-, 2-, 3-, 4- and 6-wire connections, perfect for everything from fans to fuel pumps, ignitions and anything else you want to be able to plug-in and unplug.

wiring an old car, wiring old truck, powermasterPowermaster Performance

Correct Cables

You can have the highest output alternator available, but without the proper cabling to safely and efficiently carry current to the battery, all that amperage is wasted. To safely and effectively handle the output of modern alternators, Powermaster has added a line of high-quality Charge Cables.

wiring an old car, wiring old truck, powermasterThese cables are made up of hundreds and even thousands of strands of pure copper wire so more current can be transferred efficiently with less heat buildup and loss. Even with the high number of wire strands, the cable remains very flexible, so it is easier to route through the engine compartment. The Cables are available from 8- to 0-gauge diameters in lengths from 2–12-feet, with hydraulically crimped terminals already installed. The cables meet American Wire Gauge specs, are made in the USA, and are available in red or black sleeves.

Tech Tip #3

wiring an old car, wiring old truck, fuse panel

Before purchasing a wiring harness, make sure to understand how many circuits your project will require. All of the harness manufacturers base their fuse panel on a number of circuits to handle EFI, fans, power windows, seats, HVAC, wipers, lighting, etc. This example is a stripped down nine-circuit system from American Autowire for a bare-bones hot rod.

wiring an old car, wiring old truck, speedway motors harnessSpeedway Motors

Smart Start

Do yourself a favor and invest the time and a few bucks to install an all-new wiring harness in your classic cruiser. Old wiring isn’t up to the demands of modern electronic controls and accessories, so the best way to keep the electrons flowing around your hot rod is with a new wiring harness – and you’ll be surprised at just how affordable a new harness can be.

Speedway Motors offers a 22-circuit harness that is perfect for any number of modern-day builds running electric fan(s), fuel pump, EFI, HVAC, and more. The wiring comprises of heavy-duty GXL wires that are clearly labeled and routed into an OEM-style fuse block. Speedway understands the intimidation of wiring, so they provide a comprehensive set of instructions along with a 125-piece grommet kit so you have no excuses about not having the right size to route your wires through!

wiring an old car, wiring old truck, ron francis wiringRon Francis

So Many Solutions

Electronics have always played a role in the world of hot rodding, but today that role has grown in importance. Ron Francis Wiring not only offers complete wiring harnesses for restos and custom builds, but also focuses on providing solutions for common questions and accessories such brake switch relays that function with cruise controls, under-hood or trunk lighting kits, and much more such as this module that allows a third brake light to function with the turn signals and as a running light.

This device wires into your LED third brake light to make it glow as a running light, yet also function as brake light. It makes the light flash when the turn signals are activated to draw the attention of drivers behind you. Another nifty device is their CR-92 Crash Sensor that will shut off an electric fuel pump in case of an accident. It’s a very unique accessory that the Ron Francis team simplified with easy installation and an important safety device.

Tech Tip #4

wiring an old car, wiring old truck, wiring grommet

Do yourself a favor and use a grommet when running any wires through any panel or drilled hole. A grommet is one of those five-cent parts that will prevent a short that could cause a troublesome intermittent issue or even a fire.

wiring an old car, wiring old truck, summit racing shrinkwrapSummit Racing Equipment

Sealing Splices

Whether you’re simply replacing a crusty bulb socket, installing an EFI system, or wiring an entire car, you’ll inevitably have to splice some wires together. If you’ve ever had to chase an intermittent electrical issue, you know how important it is to produce a foolproof, long-lasting electrical connection. If you’re a fan of soldering wires, Summit Racing Equipment can show you how to use the reliable lineman’s splice, or they offer a kit full of Heat Shrink Self-Solder Splice Connectors.

These butt-style connectors provide a reliable alternative to crimping andwiring an old car, wiring old truck, simply seal down permanently on your connection with the use of a heat gun. A little heat effectively shrinks the connector over the wires, forming a waterproof seal with incredible pull strength. The kit features terminals from 10- to 22-gauge that are organized in a sturdy, locking case.

wiring an old car, wiring old truck, painless wirePainless Performance

Wiring Ready

It’s always a good idea to have a variety of different color and different gauge wire in your garage. That way, if a wiring fix or accessory is being added and requires a little extra length, you’ll be covered. Do yourself a favor and never use a red wire to connect to ground (or vice-versa) just because that’s all you have available. Be prepared with the right size wire in the right color for the right job with bulk wire lengths from Painless.

With over three decades of building wiring harnesses and electrical accessories, Painless understands the importance of using quality wiring and offers their stranded copper core wiring in a number of lengths, diameters, and colors. Their wires are built for the long haul from the inside out with a cross-linked polyethylene insulation which is resistant to abrasion and can withstand over 275-degrees. In fact, their wire exceeds the OE specs for under-hood wiring.

Sidebar – Affordable Experience

wiring an old car, wiring old truck, affordable street rods

Chances are that you’ve strolled through the Affordable Street Rods traveling hot rod shop during one of our events. Rex Watson and his team have traveled the show circuits for years offering great deals on the best hot rod parts and experience.

Throughout these years, Rex has come across common issues with installations as well as what products work best, especially when it comes to wiring and electronics. We asked Rex for a few installation tips and products that could help produce a trouble-free hot rod electrical system, most of which are based on best practices during installation.

wiring an old car, wiring old truck,Grounds
With all of the electronics used on hot rods these days, grounds have never been more important. I recommend American Autowire’s All Copper Ground Kit. If you’re wiring your car, I highly recommend this kit so the entire ground circuit is tied together through copper – no steel parts –to produce the best ground path.

wiring an old car, wiring old truck, powermasterHigh-Amp Alternator
Whether you’re running a basic hot rod or one with EFI, cooling fans and more, I always recommend a Powermaster 150-amp alternator, or the 170-amp model that comes with Vintage Air Front Runner kits. There are a lot of microcontrollers on today’s hot rods, from A/C systems to fan controllers or EFI, and all of these systems work best with steady voltage. A higher-amp alternator is capable of delivering the current for accessories while maintaining a solid operating voltage. Plus, the alternators are built to handle the higher heat that is produced with increased output, so they will last longer since they’re not continually running at their full potential.

Charge and Ground Cables
Speaking of alternators, make sure to install a charge wire capable of handling the higher output. I’ve seen people install a high-output alternator, but use the same small-gauge charge wire, then wonder why the new alternator doesn’t work. A new heavy-gauge cable must be used to carry the high current. Also, to complete the circuit, connect a ground cable of the same size to the housing of the alternator. Powder coated brackets do not make solid ground paths.

Todd Ryden is first and foremost a car guy and admits to how lucky he is to have been able to build a career out of a hobby that he enjoys so much. He’s owned muscle cars and classics, raced a bit and has cruised across the country. With over 25 years in the industry from the manufacturing and marketing side to writing books and articles, he just gets it.