Make the Connection

Upgrading the Wiring Harness in an Early Chevelle

By Jeff Smith – Photography by the Author

It’s an unavoidable fact of life. The object of our ’60s and ’70s Bowtie muscle car affections are well past long in the tooth. They are well past silver anniversaries and are sneaking up on 60 years of extended service. Time tends to take its toll on items that we often take for granted—like the electrical system.

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Another fact of muscle car life is that electrical systems also suffer some of the greatest abuses. Electrical hacks, botched wiring attempts, cheesy add-on mistreatment, and a host of other sticky black electrical tape exploitation over decades of modifications have left these machines often in need of attention.

American Autowire kits
Displayed here are two different American Autowire kits. The one on the left is the Power Plus 20-circuit universal that will be used in the story. The kit on the right is the Classic Update kit for ’64-67 Chevelles that employs the same fuse box and alternator charge wire upgrade but also includes a new ignition switch along with the headlight and dimmer switches with pre-wired connectors. American Autowire also offers an OEM replacement harness that uses the original glass-style fuse block.

In our case, it was the same ’67 Chevelle that we just finished enhancing with a 5.7L LS engine and 4L60E swap. The mechanical conversion was complete and the car ran sweet, but allowing it to sit for more than six hours would put a serious drain on the battery. While repair was certainly possible, the decision was to delouse the machine completely in favor of a brand-new American Autowire electrical harness.

Read more about this Chevelle: A Rare Big-Block-Powered Two-Door Chevelle Wagon

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Most car guys abhor electrical work. It’s not difficult but it is time-consuming if you want to do it correctly. Car owner Eric Rosendahl opted for the Power Plus universal American Autowire 20-circuit kit for his Chevelle since he’d already revised so many portions of the electrical system, so that the specific Classic Chevelle kit offered numerous areas that were no longer needed. There are advantages to both systems, so it’s worthwhile to review each before making a decision.

Six-gauge alternator charge wire
The feature we really like with both American Autowire kits is this six-gauge alternator charge wire that includes a pair of 175-amp fuses. One fuse covers the charging system while the second protects the rest of the vehicle.

As an example, the Chevelle’s LS swap (detailed in an earlier issue) using a factory GM ECU required separating the starting circuit from the factory harness after the ignition switch and running it through the 4L60E transmission’s integrated neutral safety switch. Plus, the ignition side of the circuit was also changed, so for these and other reasons,  Rosendahl elected to go with the Power Plus 20-circuit universal package.

What makes American Autowire’s universal Power Plus and Classic harness systems of greater interest is the inclusion of a pair of large 175-amp fuses. These fuses protect the entire vehicle with one integrated into the alternator output circuit while the second guards the rest of the electrical system. This is far and away superior to the rather minimalistic protection offered by the original factory harness. The large six-gauge wire offers the alternator a more efficient way to charge the battery that will also do a great job of powering all the added electrical items.

Six-gauge alternator charge wire
The feature we really like with both American Autowire kits is this six-gauge alternator charge wire that includes a pair of 175-amp fuses. One fuse covers the charging system while the second protects the rest of the vehicle.

The universal kit also includes new headlight and dimmer switches. The universal kit only offers two new headlight plastic connectors, so for an early Chevelle two more new ones would be needed unless you reused the originals. The low beams use a three-pin connector while the highbeams are a two-pin.

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There’s also a six-way power accessory plug outlet in both the Power Plus and Classic Update kits that provides six, fuse-protected 15-amp circuits that could be used for any number of different dash or interior aftermarket accessories. For example, if you wanted to power up an adapter for charging a cell phone from the console, this could easily plug into this circuit.

twin fused system schematic
This schematic reveals how the twin fused system is wired into the car. The six-gauge alternator charge wire is acceptable up to 150 amps as long as the length is less than 5 feet.

This Chevelle had previously been treated to a Shiftworks electric gauge conversion that duplicates the original ’67 Chevelle dash gauges that are now all electric.  Rosendahl decided to add a 12-pin connector to allow simple connection between the instrument cluster and the rest of the harness. This would accommodate all the connections to the rear of the cluster that could also incorporate the dash warning lights. The American Autowire Chevelle Classic Update kit is already pre-wired for an instrument cluster single-disconnect connector as well as a pair of underdash courtesy lights that  Rosendahl also added for his car.

Rosendahl had previously added a headlight relay kit from another manufacturer so that required only re-wiring one headlight connector since the other three (the other low beam and the two high beams) were previously re-wired. A headlight relay kit is a great addition to any older Chevy since relays reduce the voltage drop that occurs in the stock circuit where power has to run up to and through the headlight switch and then all the way back to the headlights. With a relay kit, power is fed by the relays directly to the headlights. This means the headlight switch only triggers the relay, which greatly increases voltage to the headlights, making them brighter.

American Autowire Classic Connector
Unlike some generic harnesses, the American Autowire Classic kit comes with many of the connectors like this ignition and headlight switches already terminated and ready to plug in. Rosendahl’s universal Power Plus did not include the ignition switch connector so he reused his, which was in good shape. Often, this connector is melted from excessive current flow so that’s a consideration when choosing a harness.

With the fuse box mounted to the firewall,  Rosendahl then routed the wires through the firewall with a protective grommet and also directed the wires to the rear of the car. He started by working from the front of the car rearward. This kit offers one power lead for the windshield wipers, so  Rosendahl decided to keep the original connectors but added new wires at the wipers. Windshield wipers operate by completing the circuit to ground.

Take a look at this Render by Travis Highlander: 1969 Chevelle – Vehicle Build by Grind Hard Garage

Many of the circuits that will need new connectors, like the headlights, windshield wipers, and other components, such as an HEI distributor (for a small- or big-block Chevy engine, for example), use what is called a Packard Type 56 female connector that fits inside specific holders. These female connectors require two crimps for each wire connector. The first is the wire crimp and then there is a second crimp that captures the wire as a strain relief.

hydraulic crimp tool from Harbor Freight
To complete the large six-gauge crimp connectors, Rosendahl used this nice hydraulic crimp tool from Harbor Freight. This is not essential, but it makes crunching these large connectors very easy. It offers separate arbors for 0- all the way down to 14-gauge wire.

American Autowire sells a single- and double-wire crimping tool but  Rosendahl used his blue handle crimping tool purchased online. American Autowire’s website includes a video that runs through the steps necessary to perform a professional wire crimp that is worth the time for details on how to create the proper crimp. These crimps may require a little more effort, but the results are definitely worth the time.

Because  Rosendahl is using the universal kit, the rear wiring harness uses long, un-terminated wires to the rear of the car. He elected to reuse the original factory ribbon harness along with the taillight/brake light sockets and other connectors because they were in decent shape. He merely spliced the new harness wires upstream of the factory ribbon harness connector to the rear. American Autowire does offer new taillight sockets individually and are the same ones used in the Chevelle-specific Classic Update kit.

removing dash from the Chevelle
To make this job much easier, Rosendahl removed the driver seat, steering wheel, and dash from the Chevelle to allow easy access for wiring convenience and also to mount the new fuse box to the firewall.

One of the other advantages of the American Autowire kit is that it also eliminates the need for that clunky factory mechanical horn relay since the kit uses a more modern electronic horn relay located under the dash. We’ve found that replacing the factory horn relay with a twin-post, insulated power source for switched power offers a convenient place to pull power from under the engine compartment.

The American Autowire universal Power Plus harness does not come with a pre-wired terminal for the ignition switch, so Rosendahl decided to reuse his original ignition switch plastic connector because it was in good shape. However, many ’60s GM cars we’ve seen suffer from a melted connector as a result of resistance in the starter circuit. In this case, new connectors and a new ignition switch would be worthwhile investments. The American Autowire Classic update kit includes the parts and comes pre-wired.

Mounting the fuse block
Rosendahl wanted the fuse block wires to exit to the right, so he angled the fuse block counterclockwise close to where the original fuse box was located but farther outboard. This angle allows the wires exiting the fuse box to more easily transition to their respective areas.

In many cases, it might be advantageous to mate two wires together. The Power Plus universal kit supplied a pile of the blue insulated butt connectors that can be used for this effort.  Rosendahl prefers to use a non-insulated butt connector that is insulated with a short length of heat shrink tubing. This produces a much cleaner look and a much more professional appearance.

The universal kit supplied a generic steering column adapter so  Rosendahl purchased an adapter that should have converted this ’67 column to the later-model column connector used in the Power Plus harness. However, this separate conversion connector also did not work so the ultimate solution was to remove the factory steering column connector and re-pin a long, 16-pin black connector with the small thin pins supplied with the kit to the main harness. This only required another 10 minutes and presented no real challenge.

two-position crimp
We will skip the instructions for a two-position crimp and just show you the result. Note that both the wire and the insulator crimp fold the connector over, so each end of the crimp creates an “M” shape and do not overlap. American Autowire offers a comprehensive step-by-step video that shows how to make this crimp. This really requires the correct tool to create the proper crimp.

With the dash reinstalled in the car, we connected the battery and instantly discovered a current draw as evidenced by a small spark when connecting the positive battery cable. We used a test light connected between the positive battery cable and the positive post on the battery that will light anytime there is an electrical draw. Rosendahl then began removing individual fuses until we traced the draw to the brake light circuit. At first we thought the brake light switch was misadjusted, but the brake lights were not on.

Check out this LS Chevelle Swap: Part I: Details on Replacing a Small-Block Chevy With an LS and 4L60E

Then  Rosendahl discovered that the dome light circuit is tied into the brake light circuit (non-switched power) and since both doors were open that was the source of our current draw. We closed the doors and the test light went out! We felt a little silly but also good because all the other circuits worked perfectly. A couple of days of driving the car now confirm that the battery drain problem and intermittent circuit failures are gone and all the electrical circuits work far more efficiently. Plus, now with new LED dash instrument cluster bulbs, the dash now is more than bright enough to actually read at night.

1967 Chevelle American Autowire kit Mag Daddy magnetic zip tie
In order to de-clutter the underdash area, Rosendahl used a collection of Mag Daddy magnetic zip tie holders that allow him to quickly position a holder on the firewall or dash panel and zip tie a bundle of wires. These holders are rated at 20 pounds of holding strength and will easily retain this wire bundle for the life of the car.

Rosendahl took his time working on this project mainly by himself and was able to bring the Chevelle back to better than stock in roughly about three days of effort. Beyond just improving the electrical circuits in his Chevelle and not having to stress over forgetting to disconnect the battery, there’s also that sense of accomplishment with a job completed to your own satisfaction. That alone makes the effort and expense worthwhile. ACP

1967 Chevelle American Autowire kit LED lights
Chevelles are notorious for dim dash lights, so Rosendahl trashed the stock bulbs in favor of a set of LED lights from a company called Super Brite LED. If you want to convert the tail and brake lights to LED, keep in mind you will need an LED-compatible flasher as well.
3M makes many outstanding products, but in our opinion these Scotchloks are not one of them. We’ve seen multiple wiring problems that we’ve traced to this connector that actually cuts into the wire. We uncovered several of these critters lurking in the Chevelle’s original harness.
1967 Chevelle American Autowire kit 12-pin connector
Rosendahl decided to include a separate 12-pin connector to incorporate all the circuits present in the instrument cluster. He wired all the dash lights in series and also included power and ground along with the turn signals, high-beam indicator, but none of the warning lights.
1967 Chevelle American Autowire kit adapter
Chevrolet added an emergency flasher to the column in 1967 so Rosendahl’s column harness did not match up to the American Autowire adapter. However, a universal connector included in the kit did line up, so Rosendahl removed the factory column connector and re-pinned it into the new connector to mate to the main harness.
00 multi-strand battery cable
To complete the electrical upgrade, Rosendahl also added large, 00 multi-strand battery cable with new copper ends to increase amperage to the starter motor. We used a Moroso hammer-style crimping tool for the copper ends available through Summit Racing.
1967 Chevelle Reinstalling The Dash
The new 12-pin connector for the instrument cluster made reinstalling the dash much easier. The only electrical connections were the 12-pin instrument, headlight, ignition, stereo power, and antenna, and the single-pin cigarette lighter.
1967 Chevelle American Autowire kit Install
With the dash back in place, Rosendahl tested all the circuits and the entire system worked exactly as intended. The engine starts and runs like always and with the courtesy lights and the LED instrument cluster, the interior is far more illuminated. Plus, all the exterior lights work, even the backup lights.
Parts List
Description PN Source
American Power Plus 20 Universal kit 510008 American Autowire
American ’64-67 Chevelle complete 500981 American Autowire
American Steering column wiring adapter 36882 American Autowire
American single-wire crimp tool 510585 American Autowire
American double-wire crimp tool 510586 American Autowire
American Autowire courtesy light kit CH1748 American Autowire
Harbor Freight hyd. wire crimper, 0-14 gauge 66150 Harbor Freight
Moroso battery cable crimp tool 62262 Summit Racing
Zip tie kit 940047 Speedway Motors
Split woven loom, ¼ inch 910458014 Speedway Motors
Mag Daddy magnetic zip tie holder, set of 5 91062422 Speedway Motors
Standard Motor ignition switch US43 RockAuto
LED dash light bulb BA9S Superbrite LED
LED dome light bulb 578 Superbrite LED
Twin post electrical terminal block 555-10521 Jegs
Moroso battery cable crimp tool 62262 Summit Racing

American Autowire

Harbor Freight

Magdaddy USA
(847) 719-5600

Speedway Motors
(855) 313-9173

Superbrite LEDs
(866) 590-3533

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