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I have installed an aftermarket stereo with an amp and a active sub.

Car is a 2014 Challenger RT that had a 130 basic head, no factory external amp.

Clarion 4 channel 300w micro amp powering infinity Kappa front to back.

Sub is a Rockville 12" 400w rms active

Joying 8" double din

I didn't have any issues before the amp installs with noise in the system... I can hear the power steering, verious weird sounds from the car and slight motor noise coming through the speakers...

When I installed it, I made sure I had very good ground to each component using 8GA wire as short as possible.

Immediately I knew I had a ground issue, and set out to make sure I find and eliminate it... I thought for sure that one of my ground points was not a good ground... Tested with my multi meter, and was surprised they are the best possible points. Which I thought they would be, but didn't test before. So I took them off and made sure there wasn't an issue, and reinstalled, tested the wires and all was, and is good there.

So next I checked the factory wire harness (car side) ground to chassis ground, had a weird reading, but was checking good.

So all I could think of was to ground the stereo box to the chassis, and ground my RCA outputs to the HU box. That eliminated a lot of the noise... I could turn the radio on, and actually here the difference when making contact with the frame of the HU. But, the notice is still subtley there.

So, here is the weird part... When I have the power on the radio, and check the ground from the frame of the radio to the ground mount point on the multi meter, it reads in the -1.5 ohm range.... Why negative... Is that unusual?

I've never had to go this far to remedy a noise issue... Usually what I did, takes care of it all. I never had to pull the multimeter out.

The other odd thing was, when I checked the factory stereo harness ground, car side, to chassis ground I mentioned above it didn't a great reading. But this Canbus crap throws me off. I don't know what's what when it comes to that..

My next move was to bypass the harness Canbus ground and hook the HU ground to chassis... Is that okay to do on a Canbus car, or is that going to mess with something.?

So, my 2 questions,

Is it okay to bypass the factory stereo ground and ground to chassis?

What's the deal with a negative ohm reading when either the car and or head unit is powered on? Is that normal?

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Generally speaking, a negative ohm reading means that the circuit you are measuring is not entirely passive. It has some voltage on it. Test that same point for voltage. That would of course be a different issue. Reverse your leads and see if you get a different ohm reading that way, that may indicate DC voltage, a cap in the circuit?

A Guy

Edit, just realized you said "What's the deal with a negative ohm reading when either the car and or head unit is powered on? Is that normal? ". The multimeter reads resistance using a tiny current, if the circuit is energized, you may well expect any voltage will override the meters reference current. A ground should be measured with the circuit off. Also, do you have a common ground for everything? Different ground points can cause an issue.

I can't speak to car audio systems, but it could be something other than a ground issue? Induced interference to wiring, RCA cables, etc. by positioning next to current carrying cables?

https://www.crutchfield.com/S-FsMih...car/noise_suppressors_installation_guide.html

https://www.lifewire.com/whining-noise-when-i-use-aux-input-534592

https://www.carsdirect.com/aftermarket-parts/3-reasons-why-subwoofer-amps-overheat

A Guy
 

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I would try meeting all your new system grounds at one point at the body (anywhere on the actual metal body frame) using star washers on both the head and nut sides of your bolt
 
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