checking bad grounds
 

what would be the best way to check for a bad ground ? (meter or visual)

Test light or a meter. With a meter just measure the resistance, it should be 0 ohms or dang close to it. Visual works only if there is something really corroded or broken.

Test the resistance between places that should be ground (like a wire connection or whatever) and someplace that you know is ground, like the negative battery terminal. While observing the resistance, vigorously stress/shake the connections and wires between that location and ground looking for a change in resistance. Most multimeters have a beap feature that makes a sound when the two leads are in "contact" through a circuit, you can use this to just listen for the beap to stop while you wiggle, instead of watching the readout. Keep in mind that the contact resistance of the meter will probably read around 0.1 ohms when the two leads are connected through a wire, take this as zero. A broken circuit will read some very large resistance (many mega-ohms) or the gauge won't read at all. Hope that makes sense and good luck.

take them off and clean them.

A single strand of wire from a group of conductors will produce zero resistance when checked with an ohmmeter. And that single conductor strand may create enough resistance to prevent the circuit from working properly.

An ohmmeter isn't the most appropriate gauge to measure grounds. How could you accurately measure a suspected ground connection with an ohmmeter? BTW, ohmmeters don't like live circuits. It can let the smoke out of the meter.

Use a digital multimeter and check the voltage drop (the amount of voltage loss between two points in an active circuit. Connect the voltmeter leads to either end of the circuit to measure (not including the load), then switch the circuit ON. Voltage drop should be typically less than .1 volt.

Sherwood

So maybe a megger would be better but not a lot of people own one. Hence the shaking of the wires.

Go ahead and entertain yourself with multimeter resistance games, but Warren's advice still stands as the best you will get. Our vehicles are not as young as they used to be. Many, many car problems are electrical and most of them are problems with connections, positive or negative. Do yourself a favor in terms of preventing future problems and getting the best performance from your car by cleaning and tightening these connections. Use vinegar to clean the corrosion off, then use silicon grease to coat the surfaces. This will prevent air from reaching the metal, preventing the corrosion that tends to form on electrical contacts. Take a small needle nose pliar and carefully bend the ears of the female side of 1/4" spade, Faston connections until they fit very snugly onto the male portions. Do this with all the connections you can find. Even and especially the grounds.

Then stop thinking about continuity problems in your chassis.

It must be nice to live in a black/white go/no go world where everything is sitting out exposed in front of you with no hidden components (like a non gas tight crimp) and there are no structural elements to deal with.

Like others have said clean the grounds. There aren't that many grounds on your carrera and it will probably take you more time to check them than to clean them.

+1.
Especially the hidden connection from the battery negative to the body, its well hidden.
Then there is the one from transmission to body.....................

Don't just do grounds, all connectors are prone to corrosion.
Carefully disconnect any you can find, clean, and use dielectric grease, especially on the 14-pin.
Ensure that the relays have tight pins, sometimes they get tired and need to be spread a little with a very thin blade.
Use dielectric grease. :cool:

The original question wasn't how to fix poor ground connections it was how to find them.

And it wasn't limited to cars

the problem with this is if it is a low current circuit, if just a few strands are connected as you said and the resistance is 0, it can still show .1v and you think all is good.

Well, there is ground right under your feet. :)

SmileWavy

clean all the grounds then you do not have to look for a bad one.
i assume he is not asking WHERE all the grounds are.

it still would not hurt after all is cleaned to go ahead and make some resistance checks just to make sure.

So you think he posted a question about grounds in his house on a 911 technical forum:rolleyes: 911 in 911 technical forum is not refering to an emergency but rather a model of a car.

I was giving him advice based on my experience looking for a bad ground and made the assumption that he is working on the carrera in his signature.

-Shawn

Say someone has a problem with his turn siganls not flashing. The typical 100 uA your Fluke uses to check resistance is useless to verify the grounds on the typical lamp housing.

Voltage through resistance equals HEAT!!!
Simple to check for warmer than surrounding connections.
In an extreme case....you could use a thermal imaging device.
And as my instructor said almost 50 years ago....if you are not willing to lick a connection with your tongue....it's not clean enough for electrons!!!
Bob

keep it simple,...disconnect/clean/reassemble all ground connection points...period. You should see 0 ohms, bud (essentially).

what is your "grounding" concern, BTW? (symptomatically, that is..)

Best,

Doyle