Where is the electrical ground wires on a vehicle?

Answer 1

The negative post on the battery is connected to the chassis (or frame) of the vehicle through a heavy wire. There may also be a heavy wire connected directly to the engine. In any case, the engine, frame and body are all electric ground points.

All other electrical devices in the car use the frame or engine as the ground. Some are connected directly, for example the starter motor and alternator are bolted directly to the engine. Other components are connected to the frame or body with a wire. For example, the brake lights get power (+) through a wire from the brake light switch on the brake pedal, but they are grounded (-) through a short wire that runs to the body of the car. This makes it easier to wire the car since you don't have to run a return wire all the way to the battery.

Sometimes a ground wire becomes corroded at the ground point, which can cause electrical devices to behave poorly. If a car is old and rusty, there is a good chance that some of the electrical devices may have poor grounds. For example, the tail lights may be dim. This is almost always caused by a poor connection on the ground side, rather than a poor connection on the hot (+) side. To troubleshoot this, you can use a voltmeter to check if there is a voltage drop between the device and a good grounding point. There should be no voltage between ground and ground, but if there is voltage between the ground side of the device, and a good ground on the chassis, this means that the grounding wire does not have a good connection.