View Full Version : Ground Wires

03-20-2016, 02:37 PM
Who would buy electrical wire that was made of steel or iron? If you could, current flowing through it would make a lot of heat and it would burn open. Spark plug wires use carbon as a resistor to slow down the little current that flows through them.

When you use your car body for a ground conductor, you have a steel (return) wire with high resistance. To exacerbate the situation, most of the path back to the battery from the rear lights and fuel tank depend on fifty year-old rusty spot welds.

You have seen classic cars' stop and tail lights 'change position' at a stop light. Some go out while others shine because 1157 bulbs share the same ground electrode in a bulb holder, that is poorly or not grounded. Dim headlights are due to the same cause; poor grounding.

LED replacements depend on good solid connections because their working voltage is 2.5-volts. More resistance has a profound affect on them. HID lights draw a lot more current so solid grounding needs to be there or they won't work.

Modern cars have lamp holders with their own copper ground wires. Those ground wires plug into even more ground wires as the harnesses make their way back to the battery. Also notice, your modern vehicle has a separate body ground wire at the battery, to the body metal, using a very short wire. Do not depend on engine ground for electric motors and lights.

If you are a restorer, do your classic a huge favor by running a separate copper stranded wire from the battery to the tail light housings. This wire should be bare and unbroken with crimp terminals at every branch. For example, I slide ten ring terminals on a wire and feed the wire into the passenger compartment. At the dash, I crimp one terminal and bolt it to the floor with a separate wire under the same screw that branches the dash for front door electric windows and dash lights. The wire continues along the floor with another terminal crimped and bolted at the power seats with a separate wire under the same screw going to the seats. Another for rear power windows, another for a convertible top pump motor, trunk lid light, fuel tank and finally both tail light housings.

How big should the wire be? This depends on your load. If you are running a boomin' stereo amp in your trunk or an inverter, better count on at least #8AWG. For a stock setup, #10 will do nicely.

Ever hear of electrolysis? It's also called, decomposition potential. Electric current flowing through metal promotes rust, especially when mixed with road salts. A separate ground will stop it or profoundly slow the reaction.

I run ground wires in my own classic cars. Questions? - Dave

03-20-2016, 08:18 PM
Thank you Dave for posting this kind of information.

Understanding the technical details of electrics is like rocket science to me & I'm sure to many fellow TBirders.

While I understand the basics of electric current, it's necessary to have knowledge of the "finer" details in order to do a successful repair/modification.
It's always great to have something explained in terms that are easily understood without getting too technical.

The information you have provided in this thread is very much appreciated Dave.