Is Your Classic Vehicle Grounded?

The electrical ground for your vehicle's negative ground electrical system is the most important connection. Inadequate or improper grounds can cause a variety of electrical problems. Parking, taillight, and brake lights illuminate when a power accessory is turned on. Low voltage or components not functioning. Corrosion, poor terminations, improper wire size, or loose connections can compromise these ground connections.

The grounding system of your vehicle connects the negative post of the battery to the engine, frame, and body. This connection is made with electrical wire, cable, and metal. In most cases, the battery negative post is connected to the engine block. The engine block is connected to the frame and metal body of the vehicle. Unibody vehicles offer a more complete metal-to-metal connection. Framed vehicles can have connection issues due to the rubber body, or plastic bushings and parts that bolt or screw between the frame and body. These insulating materials and corrosion can result in a break in the ground between the two, especially in a pickup truck with the rear bed. Usually, the cable from the battery to the engine block is an appropriately sized battery cable. Connections from the engine block to the frame, from the frame to the body, and from the frame to the radiator support (on vehicles with a frame) can be made with cable or automotive braided ground straps.

The braided straps offer better benefits over wire or cable. The braided construction makes them more flexible than solid wires, allowing them to withstand repeated flexing and vibration without breaking, which is ideal for connecting moving parts like an engine or hood. The design with many small strands supports higher amperage and allows greater heat dissipation than single-strand wires. They also have a large surface area, which is beneficial for low-impedance RF grounding connections and for dampening radio-frequency interference (RFI). However, their uninsulated, open-braid design makes them susceptible to water retention, which can lead to corrosion and degradation of the connection over time. An improperly connected ground strap can lead to intermittent electrical failures, and if it's not tightened correctly, it can cause issues.

Automotive Braided Ground Strap

Proper termination is critical for wires to ring terminals. First, ensure that the terminal is the correct size for the wire gauge being used. Non-insulated terminals offer better crimping than vinyl-, nylon-, or heat-shrink-insulated terminals. Double Crimp Terminals feature two crimping points. The first crimp secures the wire strands, while the second crimp holds the wire's insulation jacket, providing a stronger, more reliable connection than single-crimp terminals. In most cases, no heat-shrink or insulating materials are not required for ground connections.

Ring Terminals

Double Crimp Ring Terminal

There are many misconceptions about attaching ground straps and wires. Shade tree technicians commonly overthink, waste time, and use the wrong materials when connecting grounding applications. Connecting painted or coated sheet metal, such as body panels and the firewall, can be done with the correct sheet-metal screw. There is no need to remove the coating or paint to achieve a bare metal surface. The connection between the screw threads and the metal is made; the tight mechanical force is essential for good electrical continuity and to minimize resistance.. This mechanical force is much greater than the force between the metal surface and the terminal. An unpainted or uncoated screw must be used. When attaching to thinner-gauge metal, a fine-thread screw will prevent a loose connection. Fasteners such as clamps, pop rivets, and aluminum nut sets should never be used. For threaded applications such as engine components and frames, ensure both internal threads and bolts are clean and unpainted.

10-32 Self-Tapping Sheet Metal Screw for Thinner Gauge Sheet Metal

Proper Grounding Techniques

Improper/Poor Grounding Techniques

When grounding electrical components, it is best to connect them to ground using the shortest possible wire.

Vehicles with fiberglass bodies, such as Corvettes, sometimes have electrical components wired with longer ground wires due to their location. In this case, the total length of the wire, both positive and negative, must be added to obtain a single length for calculating the correct wire gauge to achieve the circuit's total resistance.