Automotive Electrical Grounding

A coworker and I were talking tonight, and he was claiming that there was a car where every electrical component grounded directly to the frame, instead of having the ground wire running back to the alternator. I’ve never heard of such a thing, and I don’t even see how it would be possible. (Electronics aren’t my strong suit, but it doesn’t seem to me that you’d be able to have an isolated circuit this way, and you’d run into all kinds of interference problems doing it this way.) Anybody know if this is at least possible? And what car it might have been, if it ever was done?

I have a kit car which is basically a 1960 VW beetle made to look like a 1929 Mercedes. The engine, frame, and most of the electrical is still from the original beetle, and it’s pretty much made exactly as you describe. Instead of there being a return wire for the horn, it grounds through the steering column. Instead of a return wire for any of the lights, they just ground the return to the frame. The starter grounds to the frame. The alternator grounds to the frame. On the negative side of the battery, there’s a ground strap that goes to the frame, and that’s it. No other ground wire at the battery. It’s really not that big of a deal. All you are doing is using the metal of the frame instead of the metal from a seperate wire. You’ve still got a “circuit” since you’ve got the positive wires going out and the frame coming back.

Your main enemy in this type of system is rust. If the frame rusts and you don’t get a good electrical connection, you basically lose the grounds for most of the electrical system and the car starts having really weird electrical problems, like the tail lights come on when you honk the horn type of thing. The only problem I’ve really had with my kit car is the horn. I’ve got an aoogah horn instead of the beetle meep meep horn that came with the car originally, but it’s still the original beetle wiring, which is only one wire. The return for the horn is the steering column itself. On a brand new beetle with all shiny new metal parts this wasn’t a problem, but on a 45 year old car with a few bits of rust here and there the horn wouldn’t work reliably. I ended up running a seperate ground wire up through the center of the steering column to provide the ground, and ran that wire all the way back to the battery (which in the kit car is in the front of the car, not under the seat as it was in the original beetle). All of the lights, engine, even the radio all ground to the frame. The only part I changed was the horn, and only because it wouldn’t work reliably.

The 1960 beetle was a 6 volt system. My car is a 12 volt system. The blinker module that is in it was only used in 72 and 73 beetles (IIRC), but otherwise the wiring matches the original 1960 beetle wiring scheme. It’s fairly common for older beetles to have been converted to 12 volts at some point later in their life.

Here’s a pic of my car, in case you are interested:

If you want, I can take some pics of the electrical connections and you can see how they grounded it.

Nice looking car, and I’d be interested in seeing the pics. I kind of figured that if it had been done, it would have been done on a 6V car. I remember reading something about wiring up a car so that it wouldn’t rust (I don’t remember the details, just that some kind of voltage would prevent the metal from rusting.), I wonder if whomever wrote that wasn’t somehow getting it confused with that.

I’ve never worked on a car that was any other way.

No car that I am aware of has ground wires running back to the alternator. The alternator is grounded to the engine block, and the block is grounded to the body (frame) and the battery ground lead attaches to either the body or the engine or both.
Now does every component have a ground to the body/frame right next to it?
If you are serious about the every in that statement, then pretty much any pre very late model computerized car is built that way.
If you are willing to change every to damn near all, or 98%+ than you can say every car on the road is this way.
On a modern car there are a few circuits that will carry descrete grounds. Oxygen sensors leap to mind, rather than grounding through the exhaust pipe (like they used to) they now have a ground wire that goes back to ECM and the ECM grounds the sensor.

To feed a circuit you need a power lead and a ground lead. Since you already have a metal frame (body engine) you can use that for one side of the circuit.
[li]Saves the car maker big bucks (copper is very spendy)[/li][li]allows the wiring harness to be much smaller[/li][/ul]
If you doubt this open the hood of your car. Look at the battey negitive lead. Is it the size of an anaconda? No? then every circuit in the car is not grounded there.

When I put my 66 GTO back together, I forgot to reinstall the ground strap that goes between the engine and the body. That caused me all sorts of electrical headaches till I figured out what was wrong. :smack:

What Rick said.

There seems to be some confusion here. As mentioned, the alternator would not be (and I daresay never has been) a point for grounding. The battery negative* terminal is the ultimate ground source. But the term “ground” originates from using a common medium (origninally the earth itself for certain applications) for one side of all circuits. On cars, this common medium is the frame, along with chassis and body structures connected to it, plus the engine block for components mounted on it.

I’m not enough of an electrical theorist to explain why interference is not a problem, but I know from experience that it’s absolutely not. On cars, individual wires are sometimes vulnerable to interference (usually RFI, I believe), and where that’s an issue it’s dealt with by careful wire routing or shielding.

It seems your coworker thought that this method of grounding was exceptional and remarkable. Quite the opposite - it’s the norm. The interesting exception is cars where most components (other than those on the engine) are NOT grounded to the body or frame. This is the case with Corvettes, whose fiberglass bodies don’t allow it. Perhaps he was thinking of this, but got it flipped around.

Forgot my footnote!

*Many American cars into the 50’s and British cars into the 60’s were positive ground rather than negative ground, with the positive battery terminal being the ultimate ground and individual power for components being negative.

Electrical interference comes in several forms. Capacitive or inductive coupling between circuits, EM wave emission and reception, an impedance common to two or more circuits. Routing and shielding are used to reduce the interference from all sources to acceptable levels. There are only few really low level signals in an automobile, the input stage of the radio probably being the most sensitive. The ignition system is a major source of EM radiation. By means of a lot of experience through years of trial and error, manufacturers have learned how to manage the problem quite well.

You’re right, he said alternator, and I was too tired when I posted this to think clearly.

He was talking about a grounding set up like the old oxygen sensors, where there wasn’t a ground wire running away from the component. Which I’ve seen here and there on a few components, but not on every component.

Trial and error wins again. They probably found that the exhaust manifold or pipe rust made keeping a good ground through the life of the vehicle impossible. Except for the studs and nuts, the exhaust is insulated by gaskets and rubber mounts from the engine block and chassis. If the O[sub]2[/sub] sensor is a low level signal this could cause a lot of problems with the emissions control.

It’s not so much the gaskets and rubber mounts that cause the problem. Usually a flakey signal is caused by rust on the threads of the O2 sensor itself. Unscrewing the sensor and re-installing it would often fix a car with a “bad” sensor. Truth was the sensor was fine, it had just lost its ground.
Getting back to Tuckerfan’s OP. Many components are grounded by their mounting screws. The ABS wheels sensors we were using in class, have 2 wires 1 power and the other is a signal wire. Where is the ground? Via the mounting bolt. Tail light assemblies may have a short pigtail from the circuit board to one of the mounting bolts to ground all of the lights in the assembly with one wire. Headlight assemblies are the same way. Starters are grounded by the bolts that mount them. Stuff under and mounted tot he dash usually runs the grounds from several items to a splice (a point in the harness where a bunch of wires are fused together) and then one ground wire out from there to a ground point. The heater fans we use also have a ground lead over to the body. These last two are done tht way because the dash board and the heater case are not metalic and therefore are not grounded.
The object of every car designer is to use as little wire as possible.

I’ll accept the voice of experience. Of course, it doesn’t matter how well the sensor is connected to the exhaust if the exhaust isn’t well connected to the chassis.

That POS Lincoln I had, had bundles of wire as thick as my thumb attached to each taillight bulb socket. (Damn thing should have been called an “Edsel” it was so bad.)

And with the price of copper skyrocketing, I hope nobody get’s the “bright idea” of using aluminium like Chrysler did in the late 60s/early 70s.

The exhaust manifold is bolted tightly to the engine block which is grounded to either the chassis or the battery. The O2 sensor is in the exhaust manifold. The gasket(s) between the manifold and the head don’t come into play as the studs / bolts go through the gasket and connect the head to the manifold.