Understanding Electrical System Updates on Old Cars

August 22, 2025 Our 1960 Dodge Dart station wagon developed a few electrical issues, which were sidelined for a while. That’s about to change.By Ron Ceridono – Photography By the Author

Of all the steps taken when updating a vintage vehicle, one of the most intimidating, yet often the most necessary, is updating the electrical system. The need may arise from the deterioration of the original system to the point that safety is compromised. Reliability can also be an issue, along with the inability to add electrical accessories that the vehicle was never equipped with. In our case, all these factors were true, and the solution was installing a complete wiring system from American Autowire.
One of American Autowire’s most popular wiring kits is the Highway 22 Plus system (PN 510760). It includes ignition, headlight, and dimmer switches and utilizes GXL/XLPE GM color-coded wire with labels every 3-4 inches.

In our case, the project car involved is a 1960 Dodge station wagon. Like many Mopars of the era, it does not have a conventional fuse block. Instead, circuit breakers and inline fuses are used. This makes adding electrical accessories, like air conditioning, problematic. The car also suffers from several electrical gremlins that need to be addressed. Sometimes the interior lights do not work, while at other times they come on for no reason. Additionally, an electrical drain developed that caused the battery to go dead. As a result, the wagon was parked with the battery disconnected for some time.
The Highway Plus 22 (PN 510760) fuse block offers 22 distinct circuits, including relays for the electric fan and horn and an LED flasher for the four-way and turn signals.

In most cases, the electrical issues plaguing our Dodge can be identified by removing fuses one at a time and/or disconnecting circuits to isolate the problem. Since there was only one main circuit breaker to disconnect, it couldn’t tell us much. Additionally, so much of the wiring was in poor condition that the decision was made not to repair what was there but to replace it entirely with a new harness from American Autowire.
This Classic Update harness features a modular design with wires connected to the fuse block. Compared to an OEM system, these systems provide provisions for additional electrical accessories.

American Autowire offers three wiring kits. Their Factory Fit reproduction wiring harnesses are available for GM vehicles. They are made using original engineering blueprints and are true plug-and-play replacements. In addition to a complete harness, each sub-section of these harnesses is available under individual part numbers.

 

For those looking for originality, American Autowire offers the Factory Fit series for GM vehicles. This example uses the original style of glass fuses.

Classic Update kits are designed for restomod applications and are available for various GM, Ford, and Mopar vehicles (A-body from 1967, B-body from 1968, E-body from 1970). These harnesses replace the original wiring of a specific year, make, and model vehicle. They come with the correct, original-style lamp sockets and connectors. They also include a modern ATO-style fuse box and additional circuits for options such as A/C, power windows, fuel injection, and more.
The Highway 22 Plus fuse panel is not prewired. The wires are cut to length, stripped, and then attached to the labeled, numbered, and color-coded terminals to match the wires.

For custom applications or when a Classic Update isn’t available for a particular vehicle, such as our Mopar, American Autowire offers a variety of universal wiring kits. For applications with minimal electrical demands, the Highway 15 Plus, Power Plus 13, and Route 9 kits, power is the essential item, with additional circuits available to add accessories in the future. For applications that have greater electrical needs, American Autowire offers large-capacity systems, such as the Highway 22 Plus, Power Plus 20, and Builder 19.

 

American Autowire even includes a screwdriver for the Highway 22 Plus fuse panel terminals.When selecting a wiring harness, several considerations must be kept in mind. Arguably the most important is the number of circuits required, which depends on the electrical accessories equipped in the vehicle. However, it’s essential to consider future additions to the electrical system and plan for them. Not all circuits need to be utilized until necessary; for example, adding air conditioning later will be easier if a circuit is available to power it.
This crude circuit tester was made from an old trailer clearance light, scraps of wire, and alligator clips. It was used to verify whether there was a drain on the battery.Another aspect to consider is the basic design of the harness. There are three primary types. Some kits have all the wires attached to the fuse panel, and the wires are then routed to the loads being powered, cut to length, and connected. The second style of harness has wires running from the loads, which are cut to length and then connected to the fuse panel. Finally, exact replacement factory harnesses are terminated on both ends, although some plugs may need to be installed.
With all electrical devices turned off, our tester was connected between the positive battery terminal and the battery cable. The glowing bulbs indicated that current was flowing somewhere it shouldn’t be

For our application, we chose American Autowire’s Highway 22 Plus system, which can supply all the electronics-dependent items our Dodge will be equipped with. The fuse panel includes an LED flasher, a horn relay, and a preinstalled relay for accessory circuits triggered by 12 V or a ground circuit. A preinstalled 20-amp relay can function as either a keyed 12V or ground-triggered item, and backup light feed and power wires are included. The 20-amp wiper circuit will support all aftermarket wiper systems, and the heater-A/C power source is connected to an accessory circuit to eliminate the draw from the blower motor while the vehicle is starting.


After removing the instrument cluster, the source of the electrical problem was discovered. Several wires with melted insulation leading to a courtesy light were found behind the dashboard. If left unrepaired, the car could have burned to the ground.Installing a replacement wiring harness in an older car can prevent a multitude of problems, enhance safety and reliability, and allow for the addition of modern electrical accessories. We will show you how to ensure all the connections our Dodge needs to function well next time.

 

This is the original Mopar main circuit breaker located deep behind the dashboard. The current drawn from the melted wires seemed insufficient to trip it and open the circuit.
The Highway 22 Plus system includes a pair of 175-amp Megafuses connected by a jumper (on the right). Together, they protect the main alternator feed to the starter solenoid and the supply wire to the fuse block.The included alternator connection kit enables the use of a high-amp alternator. Along with the Megafuses, there is a six-gauge wire to connect the alternator to the battery.

 

At some point in the past, the original Dodge Polysphere engine was equipped with a late 318 Mopar electronic ignition distributor and control box. They will be retained.
Unique to Mopar electronic ignition systems are dual-element ballast resistors. It will be fed by the ignition circuit in the American Autowire harness.Adequately sized battery cables are essential. American Autowire provides premade cables and kits for custom installations featuring one-gauge cable; they come with top or side post terminals.
For wiring kits that need terminal installation, American Autowire provides two professional-quality tools: a single crimper for 14- to 20-gauge wire (shown) and a double crimper for 10- to 18-gauge wire.

 

To eliminate the frame as a conductor, American Autowire’s Grounding Kit (PN (50017) features three terminal boxes connected by a six-gauge cable that attaches directly to the battery’s negative post.
Poor grounds are a common source of electrical problems. Ground straps (or cables) should be added between the engine, chassis, and body.American Autowire offers the Highway 15 wiring system (PN 510825) for applications lacking an abundance of electrical accessories.This is American Autowire’s Classic Update Kit for 1968-70 Mopar B-bodies (PN 510634). It comes with a unique remote-mounted fuse block and firewall connector.

 

The Classic Update Kit for 1967-75 Mopar A-bodies (PN 510603) includes a replacement ATC fuse panel and a prebuilt dash for use with stock or aftermarket instruments.-MR

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Source
American Autowire
(800) 482-9473
americanautowire.com