Current Issues – A Guide to Electronics, the Wiring Harness and Components
There’s something about wiring and electronics that makes many hot rodders wince at the prospect of updating a wiring harness or troubleshooting an electrical gremlin. Though often daunting, once you really sit down and read the instructions, lay out a plan of attack, and have a few small hand tools at the ready, wiring and electrical work on a vintage vehicle can actually be fun and very rewarding.
The automotive electrical system, including all its circuits and components, covers a lot of “ground,” so to speak. And thanks to the volume of late-model accessories, controls, and creature comforts, modern hot rods and muscle machines rely on more and more electronics, just like our daily drivers.
We could fill an entire issue writing about electronics, but we only have a few pages to provide some tips from the pros and suggestions to use when you’re working on your project car. What better place to start than with what may described as the most important electrical component of the vehicle: the wiring harness.
WIRING HARNESSES
The wiring harness is essentially a network of arteries carrying electrons to each circuit on the vehicle. In most cases with an aftermarket harness, a fuse block is already attached or supplied, which is where the voltage from the battery is directed to the different circuits. The fuses, which are available in several different shapes and sizes these days, provide protection for each circuit by “breaking” in the event of a short or malfunction.
The importance of the main wiring harness cannot be understated. As more and more electronic components are incorporated into hot rods it is imperative to have a harness that can support the voltage and current requirements safely. A factory harness from a ’67 Galaxie, or even a late-’70s pickup, was not designed to handle high current accessories. Not to mention the fact that we’re working with 40-plus-year-old vehicles with corrosion and wear, some with sketchy repairs from years ago, or poorly wired-in radios, CBs or accessory lighting, and who knows what else.
American Autowire’s Classic Update Harnesses are designed for specific applications, yet provide circuits for popular add-ons and modifications. This example is for the ’68-’70 AMX.
In short, replacing the original wiring harness of a classic vehicles is never a bad idea, even on a car that’s currently running and driving. Is wiring a daunting task? Yes. Is it time consuming? Yes. But it is rewarding, adds a new level of safety (when done properly!), and the wiring companies in our industry have gone through a lot of work to supply very detailed instructions that walk you through the process.
We spoke with several of the top wiring companies in the hot rod and restoration market for a few tips concerning wiring harnesses.
Choosing a Wiring Harness
Dennis Overholser of Painless Wiring explained that the first step in determining what harness you need depends on the number of circuits.
“To start, you need to know how many circuits your vehicle is going to need,” Overholser said. “If it’s an early model car with no radio or wipers, the only circuits are lighting, ignition, and a horn, but when you get into say a squarebody or Fox body, they could be loaded up with power windows, locks, cruise, and more. Every single device needs to be counted as a circuit to help determine the harness you’ll need.”
Scott Bowers of Ron Francis Wiring also recommended starting with the circuit count. “Once you get beyond the standard fused circuits that every vehicle needs, such as running lights, brake/hazard lights, horn, radio, wiper, and heater, you also need to consider additional power accessories,” Bowers said, “including those that you may add in the future such as electric fans or a fuel pump, air conditioning, power windows, power seats, power door locks, or accessory lighting. It all needs to be considered from the start.”
The Express Wiring Systems from Ron Francis Wiring are designed for specific applications yet provide additional circuits to deliver safe, reliable performance with modern upgrades.
Adding to the list of items to consider when choosing a wiring harness is the type of project you’re working on. Are you doing a thorough factory-style restoration on a classic or more of a cruiser with a modern driveline? Marc DeMontigney of American Autowire brought up the options available in a replacement harness to match the goal of your project.
For bare-bones hot rod builds, American Autowire’s Route 9 is an affordable, universal harness that allows flexibility in mounting the fuse panel and features extra-long wires to help with routing.
“A true restoration will likely not need to support modern components such as fuel injection, aftermarket A/C, or aftermarket gauge sets,” DeMontigney said. “A modified project will almost always have at least some add-on equipment, and a wiring harness designed to incorporate modifications will make for a much easier installation. Our vehicle-specific Classic Update kits are best suited for modified restorations, Factory Fit for original-restoration General Motors projects, and universal harnesses are best for full-customs or projects where a vehicle-specific kit is not available.
“Fuse box location is another big part of the same question,” DeMontigney continued. “American Autowire builds several universal systems, the most popular being the Highway series, which allows the installer to relocate the fuse box. For someone looking to smooth their firewall or mount the fuse box under a seat, inside a kick panel, or in the trunk, a modular-style universal Harness would be the right choice.”
Pitfalls to Avoid
As mentioned earlier, wiring, especially when installing a complete wiring harness, can be an intimidating task, but we’re here to tell you that once you get in the right mindset with a plan of attack, the job is completely doable by most hands-on enthusiasts. With that, we also asked for a couple words of advice from the pros:
Take Your Time: “Don’t try to hurry!” Overholser said. “Wiring is time consuming – take your time. Lay out the entire harness, make a plan of the routing, and start laying it out one wire at a time.”
Late-model engine swaps require a serious amount of wiring. Painless Wiring offers stand-alone drivetrain harnesses. These harnesses are completely independent from chassis harness. This LS swap system example features factory connectors and a fuse block with 10 fused circuits.
Read Instructions: “Wiring usually isn’t a very difficult task, but it can be a little tedious to make neat,” DeMontigney explained. “Read the instructions, stay patient, and avoid jumping ahead on a specific part of your installation even when you’re excited to get a project running. Staying organized and methodical is often the longest part of a thorough harness installation.
Keep it Serviceable: “We all want our project to look clean and simple,” Bowers said, “however, if you compromise too far, whether it’s the way you route wires or location you mount electrical items, it can come back to haunt you. It’s the classic form versus function paradigm. Serviceability is very important as well as longevity of components – build the car to last and enjoy.
Battery and Alternator
A key component to every vehicle’s electrical system is the battery. The battery’s main objective is to get the engine started, which entails the high current required for the starter, plus powering the ignition, and in many cases the electric fuel pump and complete EFI system. Once the engine is running, the alternator becomes the main source for the vehicle’s electronics.
Before delving briefly into the charging system, Jimi Day at Optima Batteries provided some tips to consider when choosing a battery.
When mounting a battery in the trunk or interior, making the move to an AGM battery is a good choice to avoid any chance of battery acid spillage. Always properly vent a battery box/mount and note the kill switch in this application; useful as a theft deterrent and helpful to prevent any small current draw during long-term storage.
“If you have a battery mounted in an enclosed area such as the trunk or interior, flooded lead-acid batteries hold more potential for spilling battery acid and damaging panels,” Day said. “AGM batteries, preferably in a sealed battery box and vented to the outside atmosphere, are the better option.
“When shopping for a hot rod battery,” Day continued, “many look at the cold cranking amp (CCA) specifications. The CCA are measured at 0-degrees Fahrenheit for 30 seconds, so unless you make a habit of driving your hot rod in such cold temperatures, don’t over-buy based on an irrelevant specification. As hot rods get more complex from an electrical standpoint, the key-off draw on the battery has increased exponentially. If that sounds like your hot rod, pay close attention to the amp hours (Ah) or reserve capacity rating of the battery and make sure it is designed for both starting and deep-cycle use.”
As for the alternator, the challenge for vehicles laden with electronics is its ability to produce enough current to keep everything functioning properly – through the entire range of rpm. This is especially difficult with modern engines that idle at low rpm and even with overdrive transmissions that cruise at 1,500rpm. Remember, an alternator’s output is not linear – it increases (to a point) as engine rpm goes up.
As current demands increase and alternators are tasked with producing higher amps, the importance of a solid ground path also grows. We’ve noticed that alternator companies are now adding ground studs to the alternator housings to ensure a quality ground connection. Remember, powder coated and painted brackets do not work well as effective ground paths.
When choosing an alternator, it’s recommended to add up the amp draw of all the electronics on your car. For modernized drivetrains, the end number may surprise you! Think about what an electric fuel pump and fan, ECU, ignition, and injectors require, then add in running the A/C blower on high while idling at 600rpm with the stereo kicking!
With that in mind, when selecting an alternator, it is recommended to consider both the idle rpm output as well as the peak output of the unit. For example, an alternator rated at 140 amps may only produce that amount above 2,500rpm (engine), and only about 70-80 amps at idle or at low-cruising rpm. Always look at output at top end and idle.
Ed Law of Powermaster put it in general terms: “The alternator supplies the water to the battery and the battery passes out the drinks to all the electronics,” Law said. “As more electronics show up, the drinks go faster and if the alternator can’t keep up, the battery will eventually pass out all the drinks and be empty. Party over.”
Remember, whenever you upgrade to a higher output alternator, be sure to replace the charge and ground cables.
Cables and Wiring
When it comes to battery cables and the alternator charge wire, this is one area where it’s time to go big! The gauge of wire used will of course vary by the current demands of your vehicle, as well as with the distance to the battery. A restored ’67 Mustang with its stock running gear is not going to need a 1-gauge battery cable, but a restomod ’67 Mustang with a fuel injected Coyote and all the modern amenities is going to require a 1/0-gauge cable when the battery is mounted in the trunk.
A rule of thumb is a 2-gauge cable, but always choose a multi-strand copper cable and since these cables are mounted to engine components, make sure the insulation is up to the task. It is also recommended to always use the same gauge cable/wire on the ground side of the circuit, even if it’s not as long as the positive side.
When wiring accessories and aftermarket components to your car, always choose a high-grade, automotive-spec wire. Automotive wiring is no place to skimp, nor are the connectors/terminals used to connect the wires.
Mounting your battery in the trunk? American Autowire offers universal battery cable kits for both side- and top-post batteries based on 1-gauge cables made of multi-strand virgin copper cables. The high-quality cables will ensure a solid connection between the battery, alternator, and harness as well as the all-important ground path!
Ron Francis Wiring recommends to use a copper, multi-strand crosslink automotive grade wire. “Crosslink insulation is far superior to any other automotive grade wire and is designed to be resistant to automotive-grade fluids,” Bowers explained. “And when introduced to heat, it will not drip off the copper wire.
A hearty insulation is very important when it comes to automotive wiring, especially with any wires routed under the hood and around the engine. Most aftermarket companies use GXL and TXL spec wiring which is a form of the crosslink insulation recommended. Both deliver excellent heat and abrasion characteristics. Quality wiring will make a difference in the long run!
Don’t settle for cheap, big-box wiring when adding accessories or harnesses. Find a good quality copper, multi-strand automotive-grade wire with a durable insulation to handle oils, fluids, and high heat.
Useful Tools and Components
We’ve only just covered the basics when it comes to the wiring harness and wiring but wanted to provide a few favorite tools and accessories that will help when you’re working on the electrical system of your hot rod.
Strip and Crimp Tools
A high-quality set of wire terminal crimpers are mandatory when it comes to wiring harness work and Snap-on can set you up with these USA-made Cutter/Crimpers. The knife-type blades provide clean, accurate stripping and will take off up to 7/8-inch of the wire sleeve while the spring-action motion increases the leverage while reducing fatigue. Snap-on offers a number of different sizes for specific wire gauges and terminal crimps to suit any wiring task.
VOLT/OHM Meter
A volt meter should be in your arsenal of tools and is probably one of the things you should carry on road trips. Volt meters will help you track down issues with wiring, confirm when things are working right (or wrong), and can be useful for resistance measurements or when checking for continuity in a circuit. While you’re at it, pick up a simple test light to easily and quickly verify voltage, a ground, or proper working switch.
Switches
When installing a new wiring harness, there is just no reason to reuse the old worn-down switches. You wouldn’t put old spark plugs or used oil in a new engine, would you? Speedway Motors offers new ignition switches, headlight switches, turn signal switches, kill switches, dimmer switches, window switches, and whatever else you may want to activate or turn off.
Junction Studs
It seems that every electronic accessory you add is supposed to be connected directly to the battery terminals. Not only does that result in a bunch of wires hanging off the battery posts, but it eventually means poor connections to the main power and ground. CE Auto Electric Supply offers several solutions, including these 350-amp, four-post Junction Studs. These heavy-duty junctions are perfect to help distribute high current wiring and can even accept 1/0-Awg cables. Once the connections are in place, a protective cover keeps the connections safe. Available in red, or a black version to keep your ground circuits clean and effective.
Grommets and Heat Sleeve
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. Summit Racing offers several handy kits filled with different size grommets, so you’ll have the right part and the right time to finish your wiring work safely. Another handy kit to have on the work shelf is their Shrink Sleeve Assortment Kit that includes a variety of diameters of heat shrink polyolefin tubing to shrink and seal connections for a professional, safe finish.
Cable Crimps
A poor battery terminal connection can result in intermittent electrical issues or the worst short possible, so when it comes to installing terminals to the main cables, be sure to use a proper crimp tool. Speedway Motors offers these bench top hammer-style crimp tools that provide the proper, long-lasting crimp. Speedway also offers a long list of helpful wiring tools.
Photos: By the author and courtesy of the manufacturers
