Rewiring a 1957 Chevy

Modern solutions for early wiring systems

Chris Petris - August 01, 2011 09:00 AM


Removing the steering column allows plenty of room to get at things. We were sure that removing the dash cluster was inevitable requiring removal of the column. All of the wiring issues were becoming apparent.


Once we could see the gauge’s wiring, we knew it was time to remove the gauge cluster to see what we were dealing with. The blue butt connectors and different color wires connected together were not a good sign.


The more we looked into things, it made sense to remove the entire harness including the fuse panel to start from scratch. This is after we sorted the wiring out and taped the bundles going to their respective locations.


The black rubber insert has a ¼-20 threaded nut captured inside it to securely fasten the fuse panel to the firewall. We used a 3/8 inch drill bit for the well nut (as they are called) then it pushes into the firewall. The well nuts work really well securing the panel and keeping water out.


Our “F” crimp wire tool securely crimps the 56-series female terminal into position. As you can see, first we crimped the terminal to the wire; now we are crimping the terminal to the wire’s insulation.


Here we are installing a 56-series male terminal into a GM single gang connector. Be careful during the male terminal crimping process. Distorting the terminal can make it very difficult to install.


This is the correct crimp on our gauge’s eye terminal. If you get too close to the end of the terminal many times the wire strands are cut. Always make sure that all of the wire strands go into the terminal. Using a terminal that is too big for the wire gauge is not good either; the crimp may not be 100 percent tight with plenty of extra room. Follow the terminal manufacturer’s guidelines on what wire gauge to use with their respective terminals.


This is the way to finish off a terminal. Heat shrink tubing is applied to the terminal and wire providing strain relief. This keeps moisture and dirt from getting into the wiring, preventing corrosion.


We are soldering our dash light wire using rosin core solder. American Autowire’s dash harness connector has the gray wire already in place for easy connection to the dash main harness.


Like the eye terminals, heat shrink tubing prevents wire damage and strain control. Electrical tape also works if tightly wound around the wiring and connections.


One of the problems was the gauges were not working. Whoever painted the rusty corroded nuts and studs made the problem worse. We install the toothed washers onto the studs to allow them to bite into the nut and give us a low resistance connection. One added benefit of placing the washers below the terminal is it prevents them from spinning when tightening.


No wonder the gauges would not work. The build-up of corrosion prevented a good ground. We wire brushed the surfaces carefully before reassembly and the 54-year-old gauges worked perfectly.


The owner wanted the red electrical tape for his red ’57. We taped the wires to keep them in order. There is no need to tape the wires from end to end. Let them breathe and relieve the inherent heat from operation.


American Autowire made the cluster installation much easier with their cluster harness connectors. Back in the day, you had to connect each individual wire and install each bulb into position. Juggling the cluster on your legs while the connections were made was difficult and it was easy to damage the dash paint.


Small things like this make the American Autowire harness nice to work with. Simply push the correct connector into the courtesy light switches.


Here we have the starter wires ready for installation. The connector makes starter installation easier. You can install the wires on the starter before you bolt it up to the engine block. The black rubber sleeve is the end of the fuse link to protect the high amp circuits.


We added a circuit under the hood that required high amperage. This connector is an uninsulated butt connector to connect our fuse link to the load wire. We will connect this fuse link directly to the starter.


To assure a reliable connection of our additional high amperage circuit’s fuse link, we used two pieces of heat shrink tubing to cover our crimped connection.


Our harness was very close to the exhaust manifold. We used some high heat sleeving to safely thread the harness between the engine block and manifold. This is what keeps you on the road.


The tale of two improperly crimped terminals. The one on the left has a decent wire crimp without insulation strain crimping. The right terminal has been crimped with pliers and no strain relief crimping. This is the kind of stuff that makes you keep a good pair of walking shoes in your ride.

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Chevrolets from the 1950s had very few options as starting the engine was the main concern. In the early years, 30 to 35 amperage generators were able to keep up with the lighting and other electrical loads. Today, adding electrical accessories to an existing electrical system should be done with a well thought-out plan.

We need to consider the additional load our accessories will put on the electrical system. What alternator output capacity do we need to maintain our late-model electrical system? Another consideration is whether the original 54-year-old wiring is capable of handling the additional load. As wire ages, it corrodes and the insulation dries out, becoming brittle or disintegrating.

Electrical current flows over the outside of each wire strand subjecting the insulation to heat. Contaminants from the atmosphere attack and eventually cause corrosion on each individual wire strand. The build-up of contaminants raises the wire resistance, thus slowing down the electrons and creating additional heat. Wire terminals used to connect the wire harness to their respective components eventually break down. The terminals are also subjected to vibration and corrosion. Every time a wire connector is pulled off of a component, chances are very good it will loosen a little bit, adding resistance. Poor connections can create voltage drops and spikes, damaging sensitive electrical components.

Granted, 1957 Chevys do not have many sensitive electrical components, but the heat created at the terminals can destroy the component. High heat from the poor connection can ruin the plastic bodied connectors. When you see plastic melted around a wire terminal, resistance has caused the excessive heat. Simply pushing the connector back onto the component’s connector is asking for trouble. The poor connection will give you grief from erratic operation. In the shop, we replace terminals that show heat damage from a loose fit. Like any piece, there are both cheap and quality terminals available. Why save a few pennies on cheap terminals that will cost you big in aggravation later?

Problem Areas

Poor connections and corroded wiring will change the wiring’s resistance and also affects gauge readings. Coolant temp and fuel gauge readings can be way off from the additional resistance. Poor performance from anything electrical can be expected when reusing old wire harnesses.

When factory harnesses are built, all the terminals have a strain relief built into the terminal. The strain relief grabs the insulation along with the wire itself to securely connect the wire. Vibration works on the wires, leaving them hanging by the wire strands themselves, which is never good. Many of the aftermarket terminals have strain relief but it is not that great. For example, the typical blue, red or yellow butt connectors have plastic protruding past the metal sleeve. When the sleeve is crimped, the plastic is designed to be crimped as strain relief. We find many that are not crimped and even when they are, it still does not really provide a substantial strain relief.

Wire harness service tools are specific for each of the terminals and connectors. There are many wire terminal crimping tools on the market so you need to make sure you have the correct one for your terminals. GM, Chrysler and Ford used what was called an “F” crimp terminal for both the wire and insulation crimping. Using a pair of pliers (needle-nose or standard) will not properly crimp the terminal. This is a good reason to buy the custom harness that has the wire terminals crimped properly and securely.

Fuse panels have changed dramatically due to the increased accessories available. The old glass fuses took up a lot of space and, as later systems used more fuses, they switched to the more compact design of today’s ATO fuse panels. The ATO fuse panel has less fuse surface area exposed to the elements, keeping corrosion off the connections. We commonly see the old glass fuse panels full of corrosion, causing intermittent loss of electrical current.

The best policy for a properly operating electrical system is to replace all of the wire harnesses (forward lamp, engine, dash main and rear). The question is, do you buy a ready-made, correct-fit harness or a semi-universal harness? There are a couple of scenarios to think about. If we were restoring to factory original specifications to be judged for correct fit and finish, the original equipment harnesses make sense. This 1957 Chevy has a late model engine with many changes from the original installation so an aftermarket harness might make sense to use. On the other hand, many of the aftermarket accessories have their own stand-alone harness to ease the installation. Our Vintage Air A/C installation has its own harness that easily connects to the existing harness. We do have to consider the alternator’s amperage output for the addition. The original ’57 harness has a puny generator light gauge output wire that would not support the A/C system.

We considered the possibility that we would add accessories later, so we went with an American Autowire Classic Update Series harness. This will handle the additional electrical load from the A/C upgrades and possibly a radiator cooling fan. We can easily add accessories in the future without major electrical wiring issues with the aftermarket harness. The new updated harness will allow easy installation of power windows, power door locks, even power seats if we desired them. One of my major concerns is how close will this update wire harness be to the original harness? We really do not want a couple of extra feet of wire on every component rolled up and tied off to something under the dash. From the look of the harness, we can custom fit as required to make a nice clean install. The correct terminals and connectors are supplied to give it that factory installed look on the custom-fit wire areas.

After working on GM cars for years, you start to know what color wire does what, especially on early cars. Pink wires are used for ignition power, dark green would be for the coolant temp gauge sender. American Autowire stayed true to this concept, making it easy to install and troubleshoot for the masses. They went one step further and have the wire’s intended use printed onto the insulation every six inches or so. Between the correct colors and wiring identification, it should make it easier to confidently install the new harness throughout your project vehicle. We do a considerable amount of wiring in our shop, including straightening out some really questionable wiring concepts. Unfortunately this ’57 project had the wire harness installed before we were commissioned to do the job. This wiring project can be done by the do-it-yourselfer with some patience and a good service manual. Specific service manuals make the most sense; GM, Ford or Chrysler factory manuals have great info.

Keep it safe

Wiring can cause fires burning your prized possession to the ground. American Autowire has stepped up to the plate by adding protection devices. American Autowire includes fuse links in their Classic Update harness to provide protection that the ’57 would not have had with the original harness. The important thing to remember is the fuse link needs to be as close to the electrical source as possible. That is why American Autowire places the fuse link at the starter where the positive cable and main power output to the harness originates.

Fuse links were installed into factory wire harnesses starting in 1967 to prevent catastrophic failure and major fires. The fuse link is a very simple device that is similar to a fuse, except the wire burns when it is overloaded. The section of fuse link wire is of a specific length and wire gauge. The wire gauge of the fuse link is less than the wire that it protects. That means the fuse link burns before the main wiring will. When a fuse link burns, the circuit should be checked for a shorted wire before replacing the fuse link. We have seen many suspect fuse link repairs simply twisting the burned wires together or worse yet eliminating them. As we said earlier, the fuse link is of a specific length (typically five to six inches) to provide proper protection. Placing a connector in the middle of a burned link would not provide the same protection you had before.


Before we start our harness install, there are a few things to consider. What alternator will we be using? Will the alternator be a one- or three-wire connector? American Autowire has the harness configured for either. Alternator amperage output should be considered to meet our electrical load. The alternator’s role is to keep the battery charged and keep up with all the electrical circuits. If we load the electrical system with A/C, electric cooling fans, rear defogger, high output sound system and additional lighting, we need a minimum 100 amp alternator. You want to have a 20 percent minimum safety factor so the alternator is not charging at full capacity at all times.

Sound systems usually do the most damage to the electrical system from hatch-backing in the parking lot so all your friends can listen to the tunes. Also, when you call it a wrap after a day at the local car show, the alternator has to work at full capacity to get the battery back to full charge. LED lighting has helped lessen the load on the charging system but not enough to drop the alternator output requirements substantially. We chose a three-wire GM alternator with 100-amp output to keep all the accessories going and easy starting.

Why one- versus a three-wire alternator?

Alternators require an initial shot of voltage to excite the field and begin the charging process. Three-wire alternators have a two-wire connector that powers the voltage regulator and excites the field. One-wire alternators have the voltage regulator powered internally and a load sensing switch that turns the alternator on when voltage increases. Voltage load sensing is related to rpm, which means most one-wire alternators require a high idle to get them excited and charging. Aesthetics is the main reason for the one-wire alternator. The three-wire GM alternator can be repaired easily just about anywhere in the U.S. You may not be able to get a pretty chrome three-wire alternator if it fails on the road but ... the three-wire alternator is available at almost any parts store in some fashion that will work. When you get home you can have the chromed alternator replaced or repaired easily.

Now that we know what amperage alternator we are going to use, wire gauge matters. Why the electrical industry sizes a 20 gauge wire smaller than a 10 gauge wire is odd to me. If we were to use a 35-amp output alternator, we could use a 14-gauge wire with a safety margin. Our 100-amp alternator should have at least an 8-gauge wire to keep resistance low during peak charging periods. American Autowire kits were explicitly designed to utilize an 8-gauge wire, but not every kit does. On the same lines, when we install our terminal on the 8-gauge wire for the alternator, it must be securely fastened. It is common to find the alternator terminal burned from a poor connection, whether caused by a loose terminal or loose retaining nut.

We went over the importance of strain relief earlier but, how can we securely fasten our alternator output terminal to our wire and provide strain relief? We prefer to use non-insulated terminals with heat shrink tubing to provide strain relief. This method also helps keep the wire from corroding at the wire connection. GM soldered many of their high-amp load terminals to the wire for added security. This makes good sense and we typically do the same after the crimping process has taken place.

What about battery cables?

Do we really need heavy gauge cables? Getting power to the starter and a proper ground is the most important part of the equation. When you go into most retail auto parts stores, they want to sell you a 4-gauge cable for a four or six cylinder vehicle. Sure they work good on your Dodge Neon or Chevy Cobalt. The problem is they make the system work hard when the engine and ambient temperature is high. They work fine to keep the battery charged but the cranking power is reduced dramatically. Large cubic inch engines at operating temperature require higher amperage during cranking.

Likewise, cable length affects gauge sizing requirements. Placing the battery in the trunk requires heavier gauge cables to lessen voltage amperage drop. We used 2-gauge cables on the ’57 with the battery in the standard underhood location. If we were to put the battery in the trunk, 0-gauge cables would be the way to go. The ground cable can also get you into trouble. An 0-gauge wire is more efficient than the steel frame of the car. This is especially important when dealing with a fuel injected car, as it can cause problems with the EFI control module. If you decide to use the frame as a ground, place a minimum 1-gauge cable securely onto the frame or the support channels on a unibody car at the rear of the car. At the engine end, be sure that at least a 1-gauge cable is used to connect the engine to the frame. Bad things happen when the engine-to-frame ground cable is left off. Transmission selector cable linkages and any other major metallic object becomes a ground path.

Our ’57’s owner wanted us to install a battery cut-off switch for shows and when the car would sit for long periods of time. This is always a good idea to prevent accidental fires and battery drain from clocks and sound system memory circuits. Even better, shut down the battery supply circuit and connect a Battery Tender while the car sits.