problem getting good ground, 03 jetta
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=104764
Printed Date: May 01, 2024 at 10:45 PM
Topic: problem getting good ground, 03 jetta
Posted By: whiterob
Subject: problem getting good ground, 03 jetta
Date Posted: May 15, 2008 at 3:40 PM
I am installing an amp in my 2003 Jetta and was doing the test of measuring the resistance of the ground. I have come up with about 6.2 ohms which is far from the ideal ground. My question is how do I find a better ground? So far I have drilled a whole and sanded down to get bare metal. The ground is secure as well. I know you can run a wire from the amp back to the battery but it was hard enough getting my power cable wired that I don't know if I can get a ground back to the battery. When doing the test I first measured the resistance of the jumper wire I used and got around 0.8-0.9 ohms. I then connected the jumper wire to the alternator case and then to the ground. This is where I get 6.2 ohms. I did disconnect the battery too. I then reconnected the negative terminal on the battery and measured it again except this time I did it from the negative terminal on the battery. I again got the same reading. Any simple ideas other then running another cable? There really is no bolts that I can easily connect it to either.
Replies:
Posted By: Matt215customs
Date Posted: May 15, 2008 at 7:32 PM
well the 0.8-0.9 ohm reading is good because that resistance is just from your jumper ground, but the 6.2 as you said is not really what we want. So as far as the vehicle ground try maybe re-grounding the battery with a peice of 4 gauge to the chassis, maybe the ground is weak? or try the the engine block or vice versa. hope you can figure it out.
Posted By: whiterob
Date Posted: May 16, 2008 at 1:04 AM
Matt215customs wrote:
well the 0.8-0.9 ohm reading is good because that resistance is just from your jumper ground, but the 6.2 as you said is not really what we want. So as far as the vehicle ground try maybe re-grounding the battery with a peice of 4 gauge to the chassis, maybe the ground is weak? or try the the engine block or vice versa. hope you can figure it out.
So basically, doing parts of the big 3 upgrade will help? I knew that it would help but what I'm worried about is that I do the upgrades and it will not be enough. Does the big 3 ugprade really make that big of a difference?
Posted By: teenkertoy
Date Posted: May 16, 2008 at 11:25 PM
In your case, it might make a huge difference. If you car has 6ohms from chassis to battery, you should be having other issues though. That's about 6x higher resistance than normal, and would have way less current capacity for anything that uses electricity including alternator, lights, etc. Since your car is not very old, having corroded or improper factory grounding seems really unlikely.
With the engine off ... If you measure voltage across the battery terminals, what do you get? If you measure voltage across the positive battery terminal and the alternator housing, what do you get? How about to another point on the chassis, maybe the front fender's sheet metal?
Do you have a digital or analog multimeter? If you touch the positive and negative leads from the multimeter together, what resistance do you get? I assume this is where you are talking about the jumper wires having 0.8 ohms.
-Justin
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Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
Posted By: whiterob
Date Posted: May 17, 2008 at 1:15 AM
teenkertoy wrote:
Do you have a digital or analog multimeter? If you touch the positive and negative leads from the multimeter together, what resistance do you get? I assume this is where you are talking about the jumper wires having 0.8 ohms.
I have a DMM. Yes, the 0.8 was what I measured for the jumpers. I thought it was kind of low because I had 40 foot of speaker wire being used as a jumper. I tried just touching the two leads of the DMM together but didn't get a steady reading. teenkertoy wrote:
With the engine off ... If you measure voltage across the battery terminals, what do you get? If you measure voltage across the positive battery terminal and the alternator housing, what do you get? How about to another point on the chassis, maybe the front fender's sheet metal?
I will try this and tell you what I get. I tried to measure some other spots in the trunk but I could getting a reading (displays "OL") so I'll try to find a spot of bare metal.
Posted By: Alpine Guy
Date Posted: May 17, 2008 at 12:30 PM
You are going to have trouble with the Jetta because they use way different ways of putting the car together than north american brands. They use a lot of glue and sealants where they join the panels so theres not much metal to metal contact. Going to the underside of the unibody will probably get your best results.
But try the big 3 first, and see what that gets you.
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2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
Posted By: whiterob
Date Posted: May 17, 2008 at 3:29 PM
teenkertoy wrote:
With the engine off ... If you measure voltage across the battery terminals, what do you get? If you measure voltage across the positive battery terminal and the alternator housing, what do you get? How about to another point on the chassis, maybe the front fender's sheet metal?
I got either 12.2 or 12.5 volts across the battery I forgot which one exactly. From the alternator casing to the positive on the battery I got 14.3 volts. Alpine Guy wrote:
You are going to have trouble with the Jetta because they use way different ways of putting the car together than north american brands. They use a lot of glue and sealants where they join the panels so theres not much metal to metal contact. Going to the underside of the unibody will probably get your best results.
But try the big 3 first, and see what that gets you.
That is probably the problem I am having. I have noticed already that there is next to no bare metal on the car. Even in the engine compartment most of the metal is painted so I cannot get a reading from that. I guess I can try the big 3 and see what I get. I was thinking I may have to do that already because I have heard that Jettas have small wire already and pretty much need it done.
Posted By: teenkertoy
Date Posted: May 17, 2008 at 5:47 PM
whiterob wrote:
I have a DMM. Yes, the 0.8 was what I measured for the jumpers. I thought it was kind of low because I had 40 foot of speaker wire being used as a jumper. I tried just touching the two leads of the DMM together but didn't get a steady reading.
I think your test equipment setup is flawed, that much speaker wire should have a little more resistance than what you measured, certainly more than one ohm. I can't imagine what would give your a lower reading than usual though. If you can't get a steady reading by touching the red and black test probes together, then any other readings you make could be flawed. I would try to fix that issue first. A measurement of "OL" means no connection whatsoever, so your trunk seems like a miserable place to find a decent ground.
whiterob wrote:
I got either 12.2 or 12.5 volts across the battery I forgot which one exactly. From the alternator casing to the positive on the battery I got 14.3 volts.
I was trying to see if there is a voltage drop from the battery to the alternator, due to excessive resistance in the grounding. The readings you have are inconclusive though, looks like you had the engine running for the second measurement (14volts). Ideally, you'll want the voltage from battery positive -to- alternator housing, and battery positive -to- battery negative ... to be the same. Both should be taken with the engine off. This would indicate a good ground from battery to alternator (and engine most likely), and then you can go from there.
Whatever you wind up doing though, best of luck to ya. I'm curious to see what you do and how it works!
-Justin ------------- Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
Posted By: whiterob
Date Posted: June 16, 2008 at 7:34 PM
I posted here previously about not getting a good ground for my amp. What I did was tested the resistance of my ground from the ground to the alternator casing. When I did this I got a reading of around 6 ohms or so.
Well I wanted to retest my ground because I didn't trust my test. I was using 40ft of 16 gauge cable for jumper wires before. This time I used a much shorter jumper cable. When I did it this time I had much different results. I had a reading of closer to 1 or 2 ohms, not taking away the resistance of the jumper cables. However, I do not trust this test because it was not giving me a consistent reading.
So my question is, is there any other way I can test my ground without doing this test? If I measured the voltage at the terminals of the amp wouldn't that tell me if my ground is good or not? I measured it right now at 14.2 volts. That was when the amp was not hitting though but when it was just on.
Posted By: jettagli03
Date Posted: June 16, 2008 at 9:05 PM
You should use voltage drops as your resistance readings instead of resistance in ohms.
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Posted By: whiterob
Date Posted: June 17, 2008 at 12:34 AM
So as long as my voltage is good I shouldn't need to worry about my ground, right?
My voltage at the amp terminals is the same as at the battery and alternator so I guess that means I am good.
Posted By: teenkertoy
Date Posted: June 17, 2008 at 1:41 AM
Yes, if you get the same voltage at battery, alternator, and amplifier ... then you're all good. Sounds like you had some issues with the test gear previously, but it sounds alright now.
I'm curious though, why did you think the ground was an issue in the first place?
-Justin
-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
Posted By: jettagli03
Date Posted: June 17, 2008 at 9:29 AM
Try a voltage drop with one lead on the amplifiers ground wire at the amplifier itself and then put the other lead on the actual grounding point and see what your voltage drop is.
Posted By: whiterob
Date Posted: June 17, 2008 at 3:27 PM
teenkertoy wrote:
I'm curious though, why did you think the ground was an issue in the first place?
I thought it was bad when I did my first test checking the resistance. That is when I got a reading of 6 ohms.
I don't really know what the issue was on the first test. The problem was that when I tried to measure the resistance of the jumpers I was using I only got a reading of 0.7 ohms or so. That was with 40 ft of 16 gauge wire so I know that was probably wrong.
Posted By: whiterob
Date Posted: June 17, 2008 at 6:39 PM
Okay, new problem. Now I think my ground is bad for sure.
I just connected my stereo and noticed that I have a ground loop. Any ideas how to get it out? I am contemplating just running a 4 gauge wire back to my battery. Any other ideas so I don't have to do this or is this my best option.
Posted By: pbguy
Date Posted: June 17, 2008 at 7:40 PM
Try a bolt that holds the seatbelt in place near the trunk. You may have to remove carpet or molding to get to it.
Posted By: teenkertoy
Date Posted: June 17, 2008 at 10:21 PM
I'm sending you a pm, check your messages.
-Justin
-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
Posted By: jettagli03
Date Posted: June 17, 2008 at 11:21 PM
Back when I had a subwoofer in my '03 Jetta I made my own grounding point underneath the rear seat and she worked great.
Posted By: whiterob
Date Posted: June 25, 2008 at 2:12 AM
Okay so I finally got my ground all set.  I not really sure how I got it to work but it does.
What I did was take my DMM and start measuring any bare metal I could to see if I could find a reasonable ground. I thought that the seat belt idea was good because it looked like a really nice spot to ground to. It was thick metal and bare as well. So I measured it with my DMM and got about 13 ohms. This was the same as I got for all the other spots I measured in my car.
What I tried next was to see if doing part of the big 3 would help. So I left my DMM on the seat belt measuring 13 ohms then went and took a wire and connected it to the negative terminal on my battery. After that I connected it to the ground on my engine block. I went back to check the rating on my DMM and got 4.3 ohms  !! I could not understand how it could make that much of a difference.
Next I went and disconnected the wire to see if it went back up to 13 ohms but it was still at 4 ohms. Then I thought that it must have just moved so it was on bare metal better so I went back and rechecked all the other spots I measured before. They were all around 4 ohms too.
So now I have no clue what the problem was but anyways I reconnected my original grounding spot and secured it tight just to see what would happen. I turn on my system and I had no ground noise. My voltage seemed pretty good as well so I'm happy because my amp works now. 
I just wanted to update those that helped, thanks again. I just have to get my TL built now and I'll be all set. I'll make sure to update you guys once that is done too.
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