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If you look under the dash of your classic car, you probably don’t see a lot of confusing wiring like in newer cars. Cars back in the 1950s and 1960s were typically wired with the bare minimum – enough circuits to manage the standard components, and not much room for adding on.
The old fusebox from 1965. Only five fuses for the entire car – it was time to upgrade.
By the end of the 1970s, a typical wiring harness included circuits for additional creature comforts such as power windows, air conditioning, power locks, and better sound systems. By the 1980s, wiring harnesses supported two to three times the amount of circuits on cars just a couple of decades earlier.
Typical upgrades on a classic car might include an audio system or an aftermarket set of gauges; the original circuitry can be adequate for these additions. Many car owners used what is called a “fuse tap” to add a wire to an existing circuit on the fusebox to power an accessory. Though it may have worked, it was not advisable because it could put too much current on that circuit.
Another common way to add a circuit was to wire it directly to the battery with an inline fuse. That was a little better, but it still created a mess with the wiring. When you really want to bring your vehicle into the 21st century, that’s when it’s time to call Ron Francis Wiring and order a complete wiring system for your car.
It really didn't take much to remove the old harness from the car. Once out, you realize there's just not much to it, and it's easy to see that overloading a circuit won't take much.
Project Track Attack has had so many new components added that the original wiring harness had been compromised far too many times. We already added one additional relay panel, and we were contemplating adding a second one to clean things up, but decided it was better to simply replace our entire wiring harness. So we made that call to Ron Francis because it was getting difficult to keep track of all the additional circuits.
If you're not sure which harness kit is right for your car, put together a list of what you've added and give Ron Francis a call. They'll point you towards the right kit, for us it was the Express Wiring System.
Which Wiring System Is The Right One?
We spoke to Scott Bowers with Ron Francis and asked what the process was to order a wiring kit. He recommended that we provide him with a list of all the electrical components that we’ve added to the car, and a list of our future plans. Each kit can be customized to accommodate your vehicle and the circuits you want.
We build into all of our wiring kits the ability to add other accessories down the road, like an audio system or air conditioning. Each of these accessories needs to have it’s own circuit to provide independent power to the components. -Scott Bowers
With just five fuses on our original fusebox, we easily tripled that when we started adding modern electronics to our car. Although the circuits we added were safely fused, they were starting to look very unsafe and unprofessional.
Continually adding components to an existing circuit can quickly overload it; adding a bigger fuse is not the proper way to solve the problem. Too much current running through the wire can cause wires to melt; the original wiring was just heavy enough to power that circuit and not much more.
There’s always someone who will say, “I’ve never had a problem with my wiring before,” and that may be true. But consider this: if you have ever seen a car on the side of the freeway, on fire, you can bet that person hadn’t had any problems before that moment, either. Don’t be that person on the side of the road just because yesterday you didn’t have any problems. Overloading a circuit is an invitation to a dangerous situation.
Sometimes it doesn't matter how careful you are. Adding a fuse block and a circuit protector will help the additional circuits, but they can quickly become a mess to deal with.
It’s better to be safe than sorry and that’s why adding a new harness kit was a better idea than continually taxing the old wires installed 50 years ago. When we started to pull the old harness out of the car, it was easy to tell that many of the wires had lost their flexibility and the insulation was hard and brittle.
The kit will handle 18-20 circuits, with two relay systems: one for the horn, the other for an electric cooling fan, or any other circuit you’d like to use it for. The fan circuit is a 30-amp circuit, but for dual cooling fans it is recommended that an alternative system is used.
The Express wiring system trumped our anemic 5-fuse harness; and every new circuit was labeled separately and packaged with its own instruction sheet. Unlike the automotive wire you can buy at your local parts store, there are several wire colors and each wire is printed with the circuit – and sometimes the destination – every few inches directly on the wire. This allows you to run your wires from one end of the car to the other, hiding them in rocker channels or under carpet, without having to mark each wire with a piece of tape.
Ron Francis sent a box with several separate sections of our new harness packaged up for the install. Each bag is labeled with the circuit and includes instructions for that circuit.
Laying out the schematic and each harness in order made it easier to follow along; planning ahead is vital.
Planning Stages And The Proper Tools
If you’ve never done any wiring projects, it would be best to have someone help you with rewiring your entire car. Although each circuit is labeled and organized, there is some crossover into other circuits. We laid out our entire project on a makeshift table in the garage and kept two boxes: the first box was everything we were going to install, the second box was everything we either discarded or didn’t need.
To make it easier to install our new harness kit, we removed a lot of trim from the dash and the rocker panels. Plastic sandwich bags helped us to keep all the screws separate, and we labeled each bag with a permanent marker. This helps avoid the dreaded scenario where you have three screws left over and you don’t know where they go. It’s happened to us all.
Organizing the project will make it go a lot smoother; set up a work area that allows you to keep track of everything. We kept the wiring schematic handy and took notes.
Bowers suggests that before tearing out the old harness, plan the installation of the new harness and fuse panel. A good idea is to get a notepad and keep notes of what you pull out, and where you plan to run some of the new wires. Figure out where the fuse panel will fit without causing interference with other components under the dash. Some street rodders will mount the panel behind the seats, and Bowers said, “Ron Francis said he kept making the wires longer to accommodate different mounting locations so that people wouldn’t get stuck with short wires.”
From a prior gauge upgrade, we had already started cutting and splicing the old harness. All of this was coming out and being replaced.
If you can get your hands on a wiring schematic for your car, that’s going to be extremely helpful; some older cars can have circuits that are piggy-backed off of other circuits. For example: our brake lamps received power from a harness attached to the windshield wiper switch. It seems odd, but having a wiring diagram was helpful in figuring out how the original circuit was wired.
Some of the wires that led into the engine compartment were vital to what we were going to connect under the dash, so we made notes on our new wiring diagram to keep track of those circuits. The instructions for the new harnesses are great, but as you might guess there are circuits that are going to change when installing a new harness.
There were three tools that were instrumental for completing this project: a good wire stripper, a set of wire cutters, and a quality crimping tool. There are a lot of crimps that need to be made, so we contacted Pertronix for their Quick Change Crimp Tool Kit (JEGS part #751-T3001). This is not the kind of job where you twist and tape wires together or pinch them with pliers; connections need to be solid and permanent, and acquiring a good crimp tool helps you crimp like a professional.
The Quick Change Crimp Tool allowed us to crimp insulated and non insulated terminals by changing the dies, for a professional looking crimp.
Up under the dash, we found out that a lot of our interior insulation was toast, so we decided it was best to replace it with the old harness out of the way. A quick visit to Classic Industries and we found every interior insulation panel in two kits. The new insulation also provided us a solid mounting location for the Drop Down kit from Ron Francis. Since we were mounting our fuse panel up high under the dash, the drop-down kit allowed us to unhook it, making it more accessible to mount new wires to the fuse panel. This Drop Down kit will save you time – and your back if you have to keep crawling up under the dash.
While we had things torn apart, we contacted Classic Industries and ordered new interior insulation panels to replace the old ones that were falling apart. This also provided us with a suitable mounting location for the fuse panel. We added extra retainers to the insulator to support the additional weight.
The largest wires getting installed were the battery cables (1 gauge) and the alternator wire (6 gauge).
Wiring And Installation Tips
We began our install with the engine compartment and decided to clean up the existing wiring so we would have a better assessment of what we are going to remove, and how much of the existing harness is unnecessary clutter. We had done quite a few modern upgrades to our underhood harness already, so the upper firewall had a bit of patchwork done to it – and it was a mess. The apron panels were home to new fuseboxes and circuit breakers, and they needed to go away.
Remember: if you have powdercoating on your alternator, make sure to ground it with an additional wire to the block. Using a mounting bolt will not provide a good ground connection.
Still, there was one more upgrade to do before digging in, and starting this project was the perfect time for it: installing a new, one-wire alternator from Tuff Stuff. The new alternator is internally regulated, meaning we could skip the alternator harness from the Express kit. For a standard alternator, the new harness includes external regulators and alternator wiring. Ron Francis included a 6-gauge wire for the alternator due to the high output. The one-wire conversion is convenient, and Tuff Stuff alternators will put out over 12 volts at idle.
Whether you plan for a one-wire alternator like we did, or a three-wire upgrade, Ron Francis wiring kits will accommodate either type. It’s important to let them know what you’re running and how many amps your alternator puts out. For a higher output like ours, Bowers sent us a 6-gauge wire to connect our alternator directly to the battery cable. Ron Francis will also help you determine when and where to connect your charge wire – remember, this is 100 amps, so connecting to your fuse panel is not going to work.
A larger set of cutters is best for the battery cables, though taping the wire and using a hacksaw will work. The Firewall Stud Insulators provide a solid battery connection, insulated from the sheet metal.
Although the Optima battery is a leaded battery, it's not a conventional flooded battery where the positive and negative plates are submerged in an acid solution. The plates are separated by an absorbent glass mat that minimizes electrolyte spillage. For that reason, an AGM battery like the Optima doesn't need to be contained in a vented box and a hold down like this one from Classic Industries is sufficient. Make a template if you have to: the bolts that go through the floor have to be accessible.
Although we don’t recommend connecting anything to the battery until the project is completely done, determining where the battery cables will be routed is very important in this process, too. With a trunk mounted battery like ours, we had to determine where to run the battery cables and how to get them through the firewall.
If you move your battery to the trunk, remember to get a proper hold down system for it. It’s no fun to go around a corner and hear a heavy thump from the trunk area.
Two kits from Ron Francis that are perfect for the battery cables are the Firewall Stud Insulators (part #FS-8 for positive and part #FS-7 for ground). These two components will also provide a good contact for other components that need a power source, as well as the connection for the Express kit lead wire. We ran our battery cables down each side of the rocker panel to the trunk mounted Optima battery.
There are a few kits to mount your battery in the trunk, and many of them are listed for the red and yellow top batteries only. We have a blue top, which is a good solid battery for vehicles that sit for periods of time, and a quick call to Optima assured us that the blue top and yellow top have the same case dimensions, so we went back to Classic Industries for a Billet Milled Battery Hold Down. This will give us a solid mounting for the battery, bolting the hold down to the floor with four bolts to keep it secure.
Once the complete job is finished it’s time to connect the battery cables and turn on the ignition key. If you followed along and took your time, the purr of the engine will tell you that you did it right.
With the battery and alternator wiring in place, we commenced on the rest of the wiring, one bag at a time, until the final bag was removed from the table. While people like Bowers, with decades of experience, can accomplish this job in a weekend, it only took us three weekends to complete the project, taking our time to make sure we did it right. As we progressed we learned a few tricks along the way and realized that planning ahead means a lot more than just laying the bags out in order.
Some of our additional tips and guidelines are below. For a first time rewiring a complete car we were happy with the results. This Garage Series was successful, because when all was said and done, the first turn of the key put power to all necessary circuits, and the car started right up. After a couple of weeks of cleaning things up and making sure the circuits were done properly, we have had zero issues to date.
For those running LEDs, be sure to order the the LED flashers from Ron Francis. These flashers will work for low amperage circuits, but it’s important to make sure that all of your light circuits are properly grounded. Older cars sometimes use the lamp housing as a ground, and older cars need to be checked for solid ground connections from the front to the rear.
Top: We left a little extra lead in the power wire when we mounted the fuse panel. It's better for the wire to be longer than too short, this will allow for any adjustments, or utilizing the Drop Down panel.
Bottom: Feeding wires through the factory retainers is easier if you use tape on the ends and pull wires through together. Zip ties are an easy way to keep individual circuits organized.
The wiring kit includes instructions for the factory-style ignition system, including where to run the tach output. There are several aftermarket systems available, from distributors to ignition controllers, and the recommendation is to follow the manufacturer's instructions. With the MSD ignition system we are using, the connections were very simple. The Digital 6AL ignition box has its own connections for the distributor and coil, so we supplied the ignition lead and used the 6AL's tach output. We also made sure we had good positive and ground connections, connecting the ignition box to the battery cable lugs we added to the firewall.
Top: Your project will start looking like a mess of spaghetti before long, but the labeled wires and keeping them looped up until you're ready to make the final connection will help.
Bottom: Connecting to the turn signal harness, we made a label to keep track of the factory switch wire colors and the Ron Francis wire colors, and connected them one at a time. Adhesive notepads are great for this.
Top: We decided to add a bulk connector to the rear lamp harness in case we have to remove part of the harness for working on the car. This type of connector can be purchased from Ron Francis in single up to eight terminals.
Bottom: Keeping the wires separated while you complete each circuit will help keep them from getting tangled. The wires are long, so make sure you have plenty of room to stretch out.
Top: Pulling wires through and around things can damage them; never pull the wires through - feed them through with one hand and guide them out with the other.
Bottom: It's nice to have extra wire length, but don't keep them much longer than they need to be. You'll find yourself trying to wrap up too much wire to fit into a tight area. Using a multimeter can help when you're making ground connections; if the signal is weak, the circuit will be weak and it can cause problems.
Top: If your old bulb housings are corroded or rusty, replace them. Many of these can also be purchased from Ron Francis or you can find them at your local parts store. New wires are so much nicer than 50-year-old wires.
Bottom: Instead of using butt-connectors on some of the lights, we opted for Weatherpack and Packard 56-type connectors - also available from Ron Francis.
As we mentioned, it took us just three weekends to complete our wiring project; with an extra set of hands and some really good planning ahead it can be done a little quicker. If this is your first time trying a project like this, Bowers had some additional advice: “Don’t be afraid to take this project on, we’re here to help and as long as you make the connections per the instructions, our techs can help you troubleshoot any circuit that isn’t working.” They designed these kits to be installed at home in a garage, so have fun and call them if you have any problems.
If you’re thinking about taking on a project like this, get in touch with Ron Francis. There are three levels of wiring kits for just about any project car, with a day’s worth of browsing on their website for additional components and accessories. You can keep up with their own projects through their Facebook page, and you can find them at many of the larger car shows and meets throughout the year.
