Many people don’t give the wiring system in their Chevelle a thought until something goes wrong. The reality is that the whole original electrical system was designed to handle less amperage draw than that of just one decent electric fan and a high-output stereo. Compounding the issue is that the resistance within the wire increases as it ages. This makes it more difficult for the wire to handle the loads it was designed for, let alone the substantially higher demands of additional electrical add-ons.
This Tech Tip is From the Full Book “CHEVELLE PERFORMANCE PROJECTS: 1964-1972“. For a comprehensive guide on this entire subject you can visit this link:
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Naturally, there are quite a few solutions available to bring the electrical system in your Chevelle up to par. And the best place to start is with an all-new harness. That may sound drastic, but considering that the factory fuse block isn’t capable of supporting all of the aftermarket add-ons you want, and that the old wiring is probably decaying and butchered, it’s a very good place to start.
Aftermarket harnesses are available in various styles to fit the different ways a performance car may be built. Some are meant to be reproductions with the same number of circuits, all original-style connectors, glass fuses, and so on. These are a good choice if you are doing a numbers-matching restoration. The other styles have additional circuits for modern electrical gadgets, such as fuel pumps, fuel injection, fans, and big stereos.
Relocating the battery to the trunk is a great project that lets you shift a chunk of weight to the rear of the car and helps unclutter the underhood area. But when you do so, you need to increase the diameter of the battery cables to compensate for the drop in amperage over the longer length of cables.
It’s also extremely wise to change to a Ford-style starter solenoid, mounted near the battery, to improve cranking performance. The original GM starter solenoid mounted on the starter draws much higher amperage and is prone to overheating.
You can overcome these problems by using a Ford-style solenoid, which draws less amperage and can be mounted away from extreme heat sources. This also increases vehicle safety, because the positive battery cable is only powered during cranking; not during normal vehicle operation.
Relays improve safety and provide higher amperage to electric components that draw larger loads. In the 1960s, every electrical circuit had the full amperage running from the fuse block to the dash, through a switch, and then to the component. Relays allow you to run low-amperage current into the car and through the switches and keep the high-amperage line running between the battery and the device as short as possible for minimal amperage drop.
In addition to using them to activate fuel pumps and electric fans, you can also install a relay or two to increase headlight brightness. Not only will you enjoy brighter lights, but it’s also a great visible proof of the improvement that comes with keeping the high-amperage line as short as possible.
Master Disconnect Switch
Depending on the type of racing you want to do with your Chevelle, the installation of a master disconnect switch might be required. These switches are mounted in the rear panel of the car and allow someone to turn off the entire electrical system from outside in the event of a crash. Shutting down the electrical system stops the engine, turns off the fuel pump, and can even stop an electrical fire. These are great safety devices and I recommend them, even if the type of racing you do doesn’t require them.
Project 1: Wiring Harness Installation
Step-1: Select Harness Kit
Painless Performance makes a large variety of wiring harnesses. The most popular for a street machine is a replacement-style harness that mounts the fuse block in the stock location and routes the wires in a manner similar to the original harness. The harness shown here (PN 10130) is a 14-circuit, remote-mount, micro-fuse version. It uses mini fuses and has a very compact fuse block, measuring 3 x 3½ x 2 inches. This lets you mount it under the dash, under a seat, in a hidden compartment, or in the trunk. It has all of the circuits required for a street vehicle and sufficient leads to power fuel injection and air conditioning. The harness also comes with two headlight plugs, but you need two more from Painless Performance or another source for 1965–1970 Chevelles. All of the headlight plugs are installed by the customer. They do not come attached to the harness. An assortment of connectors and grommets, a steering column harness connector, flashers, and a maxi fuse that protects the whole system are included.
Step-2: Lay Out Wiring and Organize
Rewiring a car with one of these harnesses isn’t difficult. The sections attached to the fuse block are divided into the primary groups and are zip-tied together. You need to organize the wires and determine where each section is routed inside the car. Since this is a universal harness, you may need to group the sections a little differently than how Painless Performance sends them. Create mini sections before installing the harness, so you know exactly which wires are routed to certain components and areas of the car.
Step-3: Determine Route of Wires
Every wire in a Painless Performance harness is labeled with the section, wire number corresponding to the instruction manual, and where the wire should be routed. This makes it much easier as you follow wires through the car. With the fuse block location selected, you can determine how you route the wires and where you may need to drill holes to pass through the floor or firewall. You can mount the fuse block to the battery box in the trunk, and route the wires through the interior under the backseat and carpet. The only wires that need to exit the interior are for the engine bay and front lights.
Step-4: Install Maxi-Fuse
The maxi fuse protects the entire electrical system. It installs in the 10-gauge primary power wire that connects the fuse block to the positive side of the battery. The use of a maxi fuse or primary fuse breaker is common in new vehicles to protect against an electrical fire or major meltdown if there is a significant short in the system.
Step-5: Install Wiring for Steering Column
The Painless Performance harness comes with two styles of GM steering column connectors, which accommodate the most common aftermarket columns. If you have a 1967 or earlier factory column, you have to retain your column connector and do some adapting. It’s fairly straightforward to determine which wire in the new harness connects to the appropriate terminal in your factory column harness. With a later-model or aftermarket column, determine which style of connector is needed and then put the terminals on the wires and insert them into the connector.
Step-6: Wire High-output Alternator
It’s a good idea to ditch the original low-output, externally regulated alternator when you are building a modern Chevelle. Generally, you want an alternator that can produce more than 100 amps to power an electric fan, air-conditioning system, fuel injection, fuel pump, and so on. You can use a 12-si style, which utilizes a case design from the 1970s, and bolts into brackets that fit on a small-block or big-block Chevy. You can also opt for a one-wire alternator, which generally requires specialty brackets to retrofit. With the Painless Performance harness, if you have an alternator that produces more than 65 amps, you need to run two 10-gauge wires from the output pole on the alternator to handle the power.
Step-7: Install Starter Solenoid
One GM circuit design that is commonly replaced is the starter solenoid. The GM design, until the last few decades, was a larger solenoid mounted on the starter in an area prone to heat soak. The M.A.D. Enterprises Start’m Up Kit includes a Ford-style solenoid and the wires, terminals, and other parts you need to install the remote-mount solenoid; it alleviates the GM hard-start problems associated with the original design. If you have a trunk-mounted battery, this solenoid can be mounted in the trunk near it; doing so provides a safety advantage as well as improved starter cranking. The large positive cable connected to the starter is only live during cranking, eliminating the risk of a direct battery short through this cable during driving.
Step-8: Install Headlight Relay Kit
There is an easy way to improve the performance of your headlights, whether you have stock 35-watt headlights or have upgraded to 65-watt sealed halogen or xenon bulb replacements. The original circuit design has power traveling from the fuse block, through the headlight and dimmer switches, and then to the headlights. Along with a long length of wire that reduces amperage through resistance, the headlight switch also reduces the available amperage. Painless Performance offers headlight relay kits for two- and four-headlight systems that remove these drops in amperage, providing more power to the headlights for brighter operation. This route also removes a relatively high-amperage circuit from the dashboard and through an old light switch for safer operation and to extend the life of the switch.
Step-9: Install Headlight Relay Kit (Continued)
The Painless Performance headlight relay kit comes with plugs to connect directly to the headlights. For activation, it connects to one of the original three-prong headlight plugs, which tells the kit when to turn on the low beams and when to turn on the high beams. The power for the relay kit should connect directly to the battery if the battery is under the hood, or to a junction block if the battery has been relocated to the trunk. Even with brand-new bulbs, wiring harness, and a headlight switch, installing this headlight relay kit makes an improvement in lighting performance. And with an older wiring harness and switch, the difference is even greater.
Step-10: Install LED Taillights
At the rear of the car, you may want to consider upgrading to light emitting diode (LED) lights. These direct-fit LED taillights are available from National Parts Depot (NPD) for all years of Chevelles. LED lights use very little power and produce very bright light. They also illuminate very quickly, changing a lazy-looking turn signal or brake light into a crisp, modern look. The kits from NPD provide a circuit board shaped to fit in the Chevelle taillight housing. They come with a plug that is meant to be inserted into the wiring harness socket, but it’s difficult to insert and turn. It may be best to cut off the plug and hard-wire it to the taillight wiring harness. LED lights last much longer than standard incandescent light bulbs.
Step-11: Install PowerBraid Loom
To make your entire wiring system look its best, you can cover the harnesses with loom. The standard wire loom is a plastic, corrugated tube with a slit that lets you slip the wires inside. This is okay, but it retains moisture and dirt. Painless Performance offers its PowerBraid loom that lets air, moisture, and dirt pass through, but provides protection for the wires against abrasion and looks nice. Individual rolls of PowerBraid are available, as well as a Chassis Harness Kit (shown) that provides what you typically need to cover exposed sections of wire in a complete harness installation.
The Painless Performance PowerBraid is easy to work with. You slip the wires in a slit that runs lengthwise, like a corrugated plastic loom. The Chassis Harness Kit includes shrink tubing and stretch tape to neatly wrap the ends and keep the loom from fraying.
Project 2: Trunk-mounted Battery Tray Installation
Step-1: Fabricate Trunk-mounted Battery Tray
An extremely popular modification for street and performance Chevelles is to move the battery to the trunk. This moves weight farther back in the chassis for better weight transfer in drag racing and a more balanced front-to-rear weight ratio in autocross and road racing. It also removes a significant amount of clutter from the engine bay. I use an Optima AGM battery, so there are no corrosive fumes to vent. If you are using a conventional battery, it must be mounted in a battery box and vented outside of the vehicle. There are a variety of battery boxes. You want one with a metal base to mount solidly to the floor, and preferably to the frame or roll cage. This one is from JEGS and is sold as a weld-in unit, so the first thing to do is weld bolts to the base to attach it to the car.
Using the metal battery-mount base as a template, determine where the bolts should be located to attach to the trunk floor in desirable locations. Make sure you’re not drilling into wiring, fuel lines, the fuel tank, or other critical components before finalizing your desired battery location. If you do not want bolt heads inside the battery mount (because they will abrade the battery) drill 3/8-inch holes and weld the bolt heads flush with the bottom of the battery tray. You can use these holes in the battery box as a template to drill your trunk floor before welding the bolts to the box. Also weld around the bottom of the bolt heads.
The top tabs on the JEGS battery box are meant to sit over a frame rail and be welded in place. If you are not installing the box this way, cut off these tabs and use an abrasive disc to round the corners of the battery box. Also use the abrasive disc to smooth the weld pud-dles on top of the mounting bolts.
Step-2: Mount Starter Selenoid to Battery Tray
A coat of paint protects the metal battery tray from rust. Install a M.A.D. Enterprises Start’m Up Kit solenoid to the battery tray, using rounded Phillips-head 1/4-inch screws to protect the battery from abrasion. Mounting the solenoid here keeps the live positive cable very short. Also mount the Painless Performance fuse block to the battery box, again keeping the primary power wires very short.
Step-3: Install Power Distribution Block
One of the issues that arise when moving the battery to the trunk is how to provide high-amperage power under the hood for accessories such as an electric fan and even the Painless Performance headlight relay kit. The solution is to install a junction block powered by direct, but protected, battery power. This trunk-mount battery helper kit from M.A.D. Enterprises includes a junction block, fusible link, terminals, shrink tubing, 22 feet of red 8-gauge Tuff-Wire, as well as 22 feet of blue and yellow 14-gauge Tuff-Wire.
Tuff-Wire uses high-quality automotive copper strands and high-temperature, abrasion-resistant insulation. If you’ve ever used inexpensive replacement wire whose insulation can nearly be removed by scraping it with your fingernail, you can appreciate how robust this wire is. The insulation is also non-flammable, and it doesn’t easily degrade if it comes in contact with gasoline or oil. The red wire in this kit provides electricity to the junction block at the front of the car; at the junction block, you can connect your higher-amperage, constant 12-volt accessories. Use the blue and yellow wires to connect the Start’m Up Kit when mounted in the trunk.
Step-4: Install Junction Box
You can add a second junction block from M.A.D. Enterprises to create a common ground for under-the-hood accessories. Both junction blocks are mounted behind the outer headlight, making them accessible but nearly hidden. The ground circuit in a trunk-mounted battery application can be created by using the frame rail or cage or both. It’s critical that the electrical systems be properly grounded and that there is a ground strap between the engine and the frame rail. Many electrical problems can be traced to a poor body or chassis ground.
Step-5: Mount Battery Tray in Trunk
If you mount the battery above the rear axle, you can build a panel later to hide this entire area. A more common location is over the passenger-side frame rail, farther toward the rear of the car. The farther back it is mounted, the better for weight transfer. If you use an open battery box (shown), NHRA requires that a rear firewall be installed of .024-inch steel or .032-inch aluminum, including the rear package tray. Alternatively, you can use a sealed steel or aluminum battery box and vent the box outside of the body. We used a group 34 Optima RedTop battery. In addition to featuring an outstanding 800 cold cranking amps, this battery features the Optima Spiralcell technology, which uses glass mat separators and spiral-wrapped lead. This design is spill-proof and resistant to damage caused by vibration, making it ideal for racing applications and severe street use.
Project 3: Master Disconnect Switch Installation
Step-1: Select Master Disconnect Switch Kit
A master disconnect switch is required by NHRA and other sanctioning bodies for vehicles with a relocated battery. They are a good safety device on any vehicle you use for competition. They don’t have to be large and ugly, however. The Flaming River Big Switch master disconnect switch (shown) is one of the best switches. It engages solidly, and is spring-loaded to snap into the “off” position once you start turning it. It is rated at 250 continuous amps. It’s sold as just the switch and mounting bracket, or with a lever kit that includes a push-pull rod kit (which includes the aluminum rod and T-handle shown here), the switch-mount bracket, and one Heim joint and aluminum block. The Flaming River lever kit is nice, but there is an even smaller rod that still meets NHRA requirements from Jerry Bickel Race Cars. This steel rod comes with a small black knob and small Hemi joint and aluminum bracket to connect to a universal switch.
The first thing to do is determine where to mount the switch and where the rod protrudes through the rear of the car. Typical installations include through the rear sheet-metal panel. Some skip the push-pull rod and just install the twist-style switch in the rear bumper. (We want to make ours as subtle as possible, as this is primarily a street car.) On a 1966 Chevelle, there is reinforcement behind the taillight to which you can mount the switch bracket, and an access hole lines up perfectly with the reverse light lens. This also lets you simply replace the lens if you want to remove the switch later. Spend sufficient time determining the switch mounting options and the alignment of the rod to make sure you only need to drill one hole.
This shows the routing of the rod and where you will mount the switch bracket. The only parts of the Jerry Bickel Race Cars kit used here were the rod, knob, and quick-release pin. The rod is cut to length once you have the bracket mounted. You also need to use a tap to thread the inside of the steel rod to thread over the Heim joint provided with the Flaming River lever kit. Also drill a hole in the aluminum switch block midway between the switch shaft and the hole provided by Flaming River. This reduces the travel of the rod, letting it stick out of the rear of the car less when in the “on” position.
Step-2: Select Master Disconnect Switch Kit (Continued)
Remove the switch from the bracket and use the bracket as a template to mark and drill the mounting holes. The mounting surface for the switch must be secure. Check your support to make sure that rust hasn’t weakened it or its attaching points. Also be careful not to drill into wiring or hit other items behind the support when drilling. Attach the bracket using lock washers to keep the fasteners from vibrating loose. Install the switch with the provided nut and wave locknut.
The switch is pinned, so it can only be installed in two positions. Install it the same way you mocked it up. Install the aluminum block and drive the roll pin into place to lock it onto the switch shaft. With the switch in the “off” position (the rod is closer to the body in the “off” position compared to the “on” position), mark and cut the rod to length. Leave a gap of just over an inch between the knob and the taillight lens so you can comfortably grip the knob and pull it into the “on” position.
Operate the switch to make sure there is no binding or interference. If you use kits from two different companies, the locknut on the Heim joint may interfer with the aluminum block. Drill a new hole, which provides the needed clearance and still keeps the movement and travel acceptable. You need to splice the switch into the positive battery cable. If you’ve installed a Ford-style starter solenoid, this is the cable that connects the battery to the solenoid. You should also install battery terminal covers over these battery cable connections to protect against an accidental short when moving items in and out of your trunk. These are available from Flaming River or an electrical supply store.
The finished installation is very clean outside the car. The small knob is barely noticeable. Both kits come with decals that say, “Push Off,” which is required on NHRA-sanctioned drag strips. You can also make a magnetic sign, which is more noticeable when you’re at a racetrack and easy to remove when you’re not.
Written by Cole Quinnell and Posted with Permission of CarTechBooks