testing vehicle ground

How exactly do you test your ground connection?

Yes there are lot's of good posts about what readings you should get, but I havent found a layman's "connect this to that, and check for this".

I.e connect the red lead of your meter to the.........

I feel foolish, because I have installed my own sound systems in the past, and feel I have a pretty good idea what to do.

However when it came to grounding something, I assumed that the component would work if grounded properly, and not work with a bad ground.

Obviously I want to check everything for the best possible ground.

What I can gather is that you undo the negative battery terminal, make a jumper wire (or use your amp power wire cause it's there already) to extend one of your meter leads.

You then touch one lead to this jumper, which is touching the alternator, and the other lead is touching your chosen ground point. This reading, minus the reading of your jumper wire should be .5 or lower.

Do I have this correct, or am I way off?  Does it matter which meter lead touches what point? And, do I use the same meter setting that I would use to measure speaker impedence?

I drive an 05 Nissan Xterra that I will be installing 2 power amps in the near future.

My owner's manual makes a point of spelling out that any accesories installed must be grounded to a sensor near the altenator, and not the chasis. Something to do with the sensor telling the altenator how much to charge the system.

Most people will say dont listen to that, just ground properly, and hey, everything is tied back to the sensor anyway.

My thinking is that there is a reason Nissan specifically stated to run a dedicated ground.

Although it will be an added expense I am thinking I should run a dedicated ground wire to this point, and ground the 2 amps with a distribution block.

Is this the right thing to do, or should I ground to chasis? Maybe the manual instructions are simply a "cover one's own butt" disclaimer?

While I have you rattention, how come it is accepted practice to ground 2 amps seperately to chasis and yet my alpine amp manuals say to ground everything to the same point?

As long as all grounds, regadless of where they are read .5 or less then wouldnt the alternator "see" them as the same point?

Ditto for the Nissan alternator sensor?

Thanks

Thanks for the replies, but I still dont know exactly how to test for ground.

So, do not disconnect the battery, connect the red (or black) probe to the alternator, and then connect the other probe to my chosen grounding point?

Minus the resistance of my extension wire, i should be looking at .5 ohms or lower?

I do not understand, reference, series, etc.

I need to know "connect the red lead to your........" , "then connect the black lead to the............."

The grounding sticky has a lot of info but not really any lay mans how to guide.

And what is the consensus on my Nissan vehicle? Ground right to where Nissan wants me to?

It doesn't matter which probe you connect to the alternator, but common practice is to use the negative probe. Again, ignore .5 ohms or lower. You want your resistance to be as close to zero as possible, however if the ground at the head unit shows .7 ohms and the ground at your amplifier shows .4 ohms, you will want to find a better ground for your head unit. If the amplifier's ground reading is higher, you will want to find a better ground for it. You are essentially looking for two things. Resistance readings as low as possible and consistent readings throughout your system.

Connect the black (negative) lead to the case of the alternator and connect the red (positive ) lead to each ground  connection you wish to measure.

If your Nissan is under warranty, do as they suggest. If you have noise issues as a result of it, then try locations closer to the respective components.

the12volt • Support the12volt.com

1.  You'll have best results using alligator clips for the meter test probes.  But using the needle probes can be done, too.  The problem is that you will see fluctuations as you try to hold the test probe against your extension wire, and a clip would secure it better and free up your hands.  The other end of the extension wire should be secured around the ground bolt of the alternator case after first loosening it, wire-brushing it and re-tightening.

2.  Since you are using an extension wire to reach the engine bay, the resistance of your meter probes will be greater.  "Zeroing out" resistance is the act of touching the lengths of the two probes together and reading the resistance on the meter.  If it is a digital meter, you might see a resistance of, let's say, 0.11 ohms.  That is called "internal resistance" and has to be subtracted from your test findings.  That is what is considered as the "reference point".  An analog meter has a variable knob that lets you zero out the probe wire resistance so that the meter needle settles on zero, which is why the12volt likes to use it over the digital meter for a resistance reading.  After the analog meter is adusted to zero, that is considered the reference point.

3.  All in all, you are trying to find the resistance through the car's chassis from point A to point B.  If point A is the chassis ground location for the amp, then point B is the final ground destination at the alternator casing.  If point A is the chassis ground location of the head unit, the chassis resistance to point B (alt casing) should be very close to the value of the chassis resistance from the amp ground.  A large difference in these two resistance measurements is an indication that one of them needs a better ground.

4.  If you are not having noise problems with your system such as engine whine, these tests are not necessary.  Just enjoy your sound system.  I have not done these tests with my personal car...never felt that I needed to.

By the way, you have asked some very good and pertinent questions here and I would consider this a good thread to be linked in the "Proper ground" topic.  If my input is off-base, as it sometimes is, I'm sure I will be corrected and I can learn from it too.

Fantastic, thats what I was looking for.

I had most of it right except for unhooking the battery terminal.

I am glad I am not the only one who has not metered the ground connection. Since I will be running ground straight to my alternator, it should be good.

As for noise, I have never had issues ever. I have always used good cables, and have run power/remote turn on seperate from the speaker/rca lines.