Gotta Dilemma

[FrEnChYII 10+ year member]

Ok, so I have been trying to decide my best, and SAFEST way to run my power and ground wire to my rear seat in my 2006 Dakota...

I was thinking of running it under the truck and through the back wall with the help of two 1/0 grommets... I'd REALLY like to not have to cut holes in my back wall if not needed, but where in the world could I hide the wire in the truck if I ran throught the firewall? I would more than likely have to cut an area for grommets.. but, can you hide 1/0 wire under the sills on the side? Also, would I have to go one wire on each side I'd assume if I did go through the firewall.

But then.... where would I run my turn on lead and RCA's? I don't want any interference... //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

Can someone help me please?!?!? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Thanks.

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[FrEnChYII 10+ year member]

Anyone? Other than..... well..... that guy?

 

[THUNDERBIRD 10+ year member]

do lt threw the cab and then run ur rcas and remote down the center of the cab

 

[smd4life 5,000+ posts]

i like to go through the space where the steering conume goes through the fire wall

 

[helotaxi 5,000+ posts]

I got two runs of 1/0 through the firewall and down the driver's side of my Neon under the carpet between the seat and the door sill. You can't tell that it's there. As far as running the RCAs, I've zip-tied them to the power wire in the past. As long as you have basically shielded RCAs, induced noise shouldn't be a problem If you're really worried about it run them down the center.

 

[.::DuD3::. 10+ year member]

i've never had a problem running my rcas with my power, so i'd say run the them together. as for the power, just look for the best hole in your firewall. it took me forever to find mine, and even when i found it, it took forever just to get the wire through.

 

[FrEnChYII 10+ year member]

How about my ground wire then? Should I run that on the opposite side of the truck? If so, I'd more than likely have to cut a new grommet out.

And helotaxi! What a surprise to see you hear! I always use to see you on SRTForums.com... haven't in a while..

 

[faulkton 5,000+ posts]

Dont run ground to the battery...just ground the amps to metal in the rear of the truck.

 

[FrEnChYII 10+ year member]

This is why I'm going battery to amp direct ground... //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

1/0 from battery to the amp will have less resistance than grounding directly to the chassis. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Chassis Ground Resistance Tests

To check car chassis resistance, connections were made at the front and rear of each vehicle in places that would typically be used by an installer, in the manner that it is usually done – paint was removed to expose bare metal and a bolt or large-diameter screw was used through a ring-terminal that contacted the chassis.

An AC current of approximately 100 A RMS at 60 Hz was passed through the chassis between the front and rear contact points and the voltage drop and current were recorded. Resistance was calculated from these values.

Data:

Yea r Make Model ` Resistance

1995 Jeep Cherokee .0028 ohms

1996 Dodge Neon .0035 ohms

1998 Nissan Altima .0035 ohms

2002 Dodge Durango SLT .0035 ohms

The values were all very similar. To put them in perspective, at a constant 100 amp flow, .3 to .35V drop would appear between the front and rear grounds in these cars. A resistance of .0035 ohms is equal to that of 14 feet of 4 ga. Wire.

Why these particular cars? They were available. They cover a reasonable range of types.

One may ask why AC current was used for the measurements. AC was used because it's easy to create very high currents at low voltages so that the actual power used is minimal. At the frequency used (60 Hz), the AC and DC resistance are virtually the same.

One might wonder whether the relationship between voltage drop and chassis current changes with varying current. To pose this question another way, is the resistance linear?

Yes, the resistance is linear - voltage drop is proportional to current at least over a 5 to 1 range; there's no "weird" behavior.

The tests were made using custom equipment (a PDF of the schematic is available via e-mail for those who would like to examine it). A step-down transformer was needed to supply a low-voltage, high-current power source. This was made by disassembling a variable autotransformer, a large toroid (doughnut) with a winding of about 200 turns. An output winding was made by passing two turns of 4 ga. wire through its center. This gave a turns ratio of 100 to one. Applying 120 V AC to the input side gives 1.2 V on the output side. The output current will be 100 times the input current.

A 200A current shunt was placed in series with the transformer output and an AC voltmeter was connected to its measurement terminals. 4 ga. wires about 26 feet in total length were added to allow reaching the front and back of the car under test. Large copper ring terminals terminated these wires. To sense the voltage drop across the chassis, a small 16 ga. wire was run along each side of the 4 ga. current-carrying wires. These connected to an AC voltmeter.

A calibration check was made with a known, high-power resistor in place of a chassis. The resistance value calculated from the measured voltage and current was within 10% of the nominal resistor value. This is close enough to suggest that the measurements made in cars are reliable and useful.

Conclusion: Roughly speaking, the chassis is equal to a 4 ga. wire. If 4 ga. wire isn't adequate for the system, the chassis ground path should be augmented with a ground wire.

The measurements made were steady-state, not transient. The instantaneous voltage drop in a chassis will depend on the peak current and can be calculated from the resistance.

What is an excessive drop from the front to the back of a car? I say two volts total, peak, under worst-case conditions. This includes the positive and negative, so, say, one volt drop each. Assume that the total resistance of positive wire + chassis is .007 ohms, then for a 2 volt peak drop, you can pull 285 amps peak. One 1000/1 will be OK, two will exceed this. Keep in mind that these numbers do NOT include voltage sag at the source, the battery + alternator. One wonders in particular what happens when the instantaneous current exceeds the alternator output.

These measurements aren't all that hard or time-consuming to do, if you have the equipment. The car doesn't need to have a system, and measurements are made with the car and all of its equipment off.

Hope that helps,

Manville Smith

JL Audio, Inc.