problem getting good ground, 03 jetta

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whiterob

Copper - Posts: 351

Joined: July 22, 2007

Location: United States

Posted: May 15, 2008 at 3:40 PM / IP Logged

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.

Matt215customs

Member - Posts: 4

Joined: May 06, 2005

Location: United States

Posted: May 15, 2008 at 7:32 PM / IP Logged

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.

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whiterob

Copper - Posts: 351

Joined: July 22, 2007

Location: United States

Posted: May 16, 2008 at 1:04 AM / IP Logged

Matt215customs wrote:

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?

teenkertoy

Copper - Posts: 112

Joined: April 01, 2008

Location: California, United States

Posted: May 16, 2008 at 11:25 PM / IP Logged

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

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.

whiterob

Copper - Posts: 351

Joined: July 22, 2007

Location: United States

Posted: May 17, 2008 at 1:15 AM / IP Logged

teenkertoy 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.

teenkertoy wrote:

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.

Alpine Guy

Platinum - Posts: 2,478

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Joined: October 18, 2003

Location: Canada

Posted: May 17, 2008 at 12:30 PM / IP Logged

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.

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.

whiterob

Copper - Posts: 351

Joined: July 22, 2007

Location: United States

Posted: May 17, 2008 at 3:29 PM / IP Logged

teenkertoy 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.

Alpine Guy wrote:

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.

teenkertoy

Copper - Posts: 112

Joined: April 01, 2008

Location: California, United States

Posted: May 17, 2008 at 5:47 PM / IP Logged

whiterob wrote:

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.

whiterob

Copper - Posts: 351

Joined: July 22, 2007

Location: United States

Posted: June 16, 2008 at 7:34 PM / IP Logged

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 o

jettagli03

Copper - Posts: 311

Joined: January 16, 2005

Location: United States

Posted: June 16, 2008 at 9:05 PM / IP Logged

You should use voltage drops as your resistance readings instead of resistance in ohms.

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