How do you find good ground with dmm? ....

[Jd377 6]

I've been searching and not finding exactly what I wanted.... Im trying to figure out how to find a good ground in my car for my rear batts and I know people use DMM's to test spots but I wasn't sure how? like which setting on the dmm and what do you touch the probes to?.. I dont understand rofl. I tried a bunch of different things but wasn't really sure what I was doing.

[jonbearsmt 919]

ohms....

the your looking for resistance.

[Jd377 6]

Alright, so I set it to ohms but then do I just touch the neg end to my Rear batt - post and then touch the other side to the point I want to test?

I touched it all over and it would go to 0.00 lots of time and if I put both probes up in the air it reads 1.00 a couple times it would say like 0.08 on a few places. Sound normal?

Can I just use the bolt that my driver seat is bolted down with to ground rear batt?.. I dont know where to ground if it has to be 3ft< because the trunk is maybe 3ft at the very beginning of the trunk so I cant reach the metal back their very easy, and im scared ill hit the gas tank if I drill the closest trunk ( right behind rear seats if I fold them down slightly )

[05Trailblazer 1]

i want to know the answer to ur questions !

[lithium 358]

Alright, so I set it to ohms but then do I just touch the neg end to my Rear batt - post and then touch the other side to the point I want to test?

I touched it all over and it would go to 0.00 lots of time and if I put both probes up in the air it reads 1.00 a couple times it would say like 0.08 on a few places. Sound normal?

Can I just use the bolt that my driver seat is bolted down with to ground rear batt?.. I dont know where to ground if it has to be 3ft< because the trunk is maybe 3ft at the very beginning of the trunk so I cant reach the metal back their very easy, and im scared ill hit the gas tank if I drill the closest trunk ( right behind rear seats if I fold them down slightly )

the < 3ft rule is mostly bullshit. just find a think piece of metal, sand it down, and bolt your ground to it. rear seat mount might work. if you want to check shit with the dmm, set it to ohms, one probe will be connected to the front battery (use a long piece of wire) and take the other probe and touch points test them (you would have to sand down each location you want to check obviously). but really if you bolt the ground to thick piece of metal, that has a solid connection to the frame, then there's nothing to worry about.

[///M5 2,833]

Path of least resistance is great, but you don't really need a DMM to understand where that is. If you have a framed vehicle the frame is a great start.

[AllenH427 10]

Not many people know of this method, but it's the absolute BEST answer and BEST method of doing it.

Here's the steps:

Take a longgggg 16/18awg or small wire and connect it on your front battery's negative terminal.

Now, pinch of other end of the wire with the positive or negative DMM probe.

Next, take the other probe and start testing bolts. Resistance will read 0 if the bolt is (technically) connected to your front batteries negative terminal.

Now, whether you're grounding and amp or battery to that bolt, you will know that it's using the same ground as your front battery!

[jcarter1885 995]

Seat belt bolts or seat bolts are not good grounds, just an fyi

[alain 6]

Seat belt bolt didn't work for me in my impreza I found that the rear shock tower was the best for my application.

[Jd377 6]

So Can it be longer than 3ft for the ground wire... I have a spot that I was using for a ground in my trunk, but my new batt location would be about ~5ft from there?.. is 5-6ft run for a ground too long...?...

[alain 6]

I think the quality of the wires play a bigger roll then the lenth I use 1/0 copper wire work good for me.from battery to my amps 6ft of wire.

[AllenH427 10]

So Can it be longer than 3ft for the ground wire... I have a spot that I was using for a ground in my trunk, but my new batt location would be about ~5ft from there?.. is 5-6ft run for a ground too long...?...

Don't take this as a definite answer, but in my opinion, I can't see it mattering. A piece of wire is a piece of wire, end to end is all one solid piece.. plus it has high conductivity. The only time I see having too long of a ground being a problem is if it's 4-5x the length of the power wire, and it still probably won't be a problem then.

Edited September 30, 2011 by AllenH427

[///M5 2,833]

If 3' were as long as the ground could be then you would say the same for power. It is a "loop" what you don't want to do is put a weak link in it.