Having an ohm reading above 5 ohms is considered to be a bad ground.
Although ideally having a good ground should be of 0 ohms resistance and anything above 0 ohms can be a bad ground.
However if you have a reading less than 5 ohms, the ground is considered okay.
To find a bad earth on a car, vehicle other equipment you should look for any signs of poor electrical connections and test the continuity of any ground wires.
You can also use a multimeter to measure any voltage drops or current leaks.
Set the multimeter to the DC voltage setting and then connect the red probe to the positive side and the black probe to the ground or negative side.
If you have a reading on your multimeter that is close to 0 volts then it indicates a good ground and if it's higher than 0 it indicates a poor ground.
Another way to test for a bad ground or bad earth on a car is to to a resistance test.
With the vehicle off, set your multimeter to measure resistance which is also known has ohms.
Measure the resistance between the ground point and the component.
A reading that is significantly above 0 ohms indicates that you have a bad ground.
Some signs that your car has a bad ground or bad earth are flickering or dimming lights, battery drainage, ignition or radio noise, or the heater blower, power windows or other accessories may work intermittently or stop functioning.
A bad ground can also cause hard starting and make the starter drag or even just the solenoid click when you turn the key.
A bad ground on a vehicle can also prevent the alternator from properly charging your vehicles battery and lead to low voltage readings and even damage the battery.
An engine needs a ground strap that is connected to the engine and then to the body of the vehicle.
And it's also recommended that the engine have another ground strap from the engine to the frame if your vehicle has a frame.
Having a ground strap from the engine to the chassis and or a ground strap from the engine to the frame helps provide for a good ground and prevents electronics such as the ignition module from burning up.
The best grounding point for a car is the engine block, as well as an additional small ground water connected to the inside fender or other metal part of the car.
The engine block and the cars chassis are excellent electrical conductor and provide for a path of low resistance for current to flow back to your battery.
You should also have a grounding strap from the engine to the body to prevent electronics such as the ignition control module from burning out.
A 12V battery does need to be grounded or it will not work as the ground wire and the positive wire have to be connected so that it can complete the circuit.
However with a 12V battery you don't need an earth ground connection like you do with AC voltage.
If on your vehicle or anything else you should also add a second small ground wire from the battery terminals negative side to the metal part of the vehicle or other thing that you have the battery connected too.
The black wire on a car battery is the ground also known as the negative with the --- Symbol.
The red wire on the battery is the positive wire which has the + symbol.
The red wire for a car or truck or automotive battery goes to the positive side of the battery which is + and the back wire always goes to the negative side of the battery which is the ---- symbol.
If you connect the battery cables wrong the battery will spark and can catch fire and it can ruin your electronics in your car.
Also make sure that the battery cables are tightened down enough to make contact and prevent starting problems and charging problems.
And make sure the battery cable ends and battery terminals are also clean and free of corrosion.
You can clean battery terminals of the corrosion by mixing some baking soda with some water and then poor it on the battery cables and allow it to sit for awhile.
Then brush the battery terminals until clean.
You can also dip the battery cables ends into some baking soda and water and allow it to sit and then brush off the battery cable ends and rinse with a bit of water.
When your battery cable ends and battery terminals are corroded it can prevent the current from flowing through the battery cables and prevent the battery from charging properly are cause a clicking sound when you try to start the engine.
If loose enough the engine may not want to start at all.