Tracking big resistance in wires, plz help

[Tophatjimmy]

I've been fighting engine whine in my stereo for quite a while now so I did some metering of my wiring.

From the battery - to the radio - is 0.4ohms
from the battery + to the radio + is 97ohms!!

I need to find out where I've got a bad connection in the circuit. Of the 4 wires at the back of the alt, one goes directly to the battery, but where do the other 3 go to??

I have a feeling this is gonna get ugly....

 

[SY2932]

Re: Tracking big resistance in wires, plz help

More than likely your problem is a bad ground somewhere. How is the connection between the negative terminal and the frame? Don't forget to check the ground that goes from the back of the driver's side head to the firewall too...

 

[Daryl H]

Re: Tracking big resistance in wires, plz help

I've been fighting engine whine in my stereo for quite a while now so I did some metering of my wiring.

From the battery - to the radio - is 0.4ohms
from the battery + to the radio + is 97ohms!!

I need to find out where I've got a bad connection in the circuit. Of the 4 wires at the back of the alt, one goes directly to the battery, but where do the other 3 go to??

I have a feeling this is gonna get ugly....

I assume that you disconnected the battery and rang through the ignition switch to read the 97 ohms.
Unfortunately I do not believe the radio will work at all with that great of a resistance. I suggest you retry that one.

Does the whine increase with engine speed?
How old is the battery/alternator?


One of the connections on the alternator goes to the junction block on the passenger side firewall.
Another one goes to the fuse block in the cab.
The last one I guess, goes to the intercooler pump relay.

 

[Whiplash]

Re: Tracking big resistance in wires, plz help

More than likely your problem is a bad ground somewhere. How is the connection between the negative terminal and the frame? Don't forget to check the ground that goes from the back of the driver's side head to the firewall too...

99% of the time it is a bad ground. GM vehicles can be a real pain with engine noise. Is your system stock? If you have any amplifiers make sure the power and ground wires and the RCA wires are run as far apart as possible.

 

[dgoodhue]

Re: Tracking big resistance in wires, plz help

I've been fighting engine whine in my stereo for quite a while now so I did some metering of my wiring.

From the battery - to the radio - is 0.4ohms
from the battery + to the radio + is 97ohms!!

I need to find out where I've got a bad connection in the circuit. Of the 4 wires at the back of the alt, one goes directly to the battery, but where do the other 3 go to??

I have a feeling this is gonna get ugly....

One goes to the IC pump, I think the other two go to the fuse block and ignition switch.

97 Ohms isn't really all that high considering its path. Your going through Fuse Block/Bulk head connector, a fusible link before connecting to the battery. I bet teh most ofo the resisitance is in the fusable link. As long as you getting plenty of voltage at your stereo, you should be fine.

 

[Tophatjimmy]

Re: Tracking big resistance in wires, plz help

The radio works fine, but unless i connect it directly to the battery posts, I have engine (alternator) whine.

I'd never run into a vehicle that I couldn't solve a noise issue until this one.

 

[dgoodhue]

Re: Tracking big resistance in wires, plz help

The radio works fine, but unless i connect it directly to the battery posts, I have engine (alternator) whine.

I'd never run into a vehicle that I couldn't solve a noise issue until this one.

Do you have aftermarket amplifiers?

 

[jpalmer]

Re: Tracking big resistance in wires, plz help

Do you have aftermarket amplifiers?

this would have been my first question on this topic. I would just make a separate circuit for your stereo anyways. i always do so there is no interference with anything else. just my :2cents:

 

[Tophatjimmy]

Re: Tracking big resistance in wires, plz help

Do you have aftermarket amplifiers?

I do, two of them, and trust me they have been thoroughly investigated.

Under 2 conditions does the noise go away:
1) using an external, self powered source (not through the head unit) to send signal to the amps. (I also wired in a completely different head unit to eliminate the head unit itself as the source of noise. No dice.)
2) I run a dedicated power and ground from the radio directly to the battery posts.


If I grab power or ground ANYWHERE else in the vehicle, I get noise. Still sorting it out....:rant:

 

[GAShan]

Re: Tracking big resistance in wires, plz help

Did you try ground loop isolators on the rca's to the amps?

 

[dgoodhue]

Re: Tracking big resistance in wires, plz help

Make sure you amps have a good ground. Measuring resistance isn't good enough for amp grounds, but what might might be a good ground to you meter (and its mA source) may not be good enough fo3 20, 30, 40 etc amps. I thought the ground in the back floor corner of my Syclone was good but I always got noise. I found out the peice after closer inpsection only have a few spot welds hold it to the cab ground. Moving the ground eliminated the engine whine.

 

[Tophatjimmy]

Re: Tracking big resistance in wires, plz help

RCA noise decouplers make it worse actually.

The amps are grounded to the frame at the same place my relocated battery is.

I think what I'm going to do is trace the 12v+ wires from the battery to their end points and check for corrosion and resistance at each stop/junction along the way. When that's done I'll move on to the ground path and do the same thing.

I've been doing this for awhile now (car audio, 7+ years) and almost never have noise issues, even when the RCA's and power wires are going down the same side of the vehicle. When i do it's usually a really quick and easy fix, but this truck is just kicking my ass all over the place....

 

[gkrcr882]

Re: Tracking big resistance in wires, plz help

Did you try using/making shielded wire to prevent the RFI? I'm not sure if there is any (factory) for the audio system or not.

 

[Tophatjimmy]

Re: Tracking big resistance in wires, plz help

Did you try using/making shielded wire to prevent the RFI? I'm not sure if there is any (factory) for the audio system or not.

The problem isn't in the signal cables to the amps, been there done that. Even ran them outside the truck away from everything and still had noise.
The noise is coming from the power or ground that the truck is providing to the stereo. The stereo is then passing that noise along to the amps and from there, the speakers.

Anyway, welcome to my frustration.....

 

[dgoodhue]

Re: Tracking big resistance in wires, plz help

The amps are grounded to the frame at the same place my relocated battery is.

I wonder if your relocated ground is the problem not your stereo. ie the engine ground is poor and it is taking a ground path back through your radio.

 

[Tophatjimmy]

Re: Tracking big resistance in wires, plz help

I wonder if your relocated ground is the problem not your stereo. ie the engine ground is poor and it is taking a ground path back through your radio.

That's on the agenda to check tomorrow.

 

[qbnkiller]

Re: Tracking big resistance in wires, plz help

If you hav access to an oscilloscope, scope the ground to the stereo. Something else to look at - do you have a CDI ignition close by to the radio? RFI? Disconnect your radio antenna and check for noise again.

 

[BoostedSUV]

Re: Tracking big resistance in wires, plz help

Check continuty between the radio case, or radio ground to the outter surface of the RCA plugs on the back of the headunit. The headunits provides a gound to the RCAs and prevents noise. I chased this same exact thing in GF's car and that was my problem. If I grounded the outer portion of the RCA cable the noise went away. I ended up taking apart the headuint and solder a wire from a ground source on the circuit board to the ground for the RCA outputs. Worked like a charm. You should have zero resistance from the headunit case to the RCA output on the outter part. Just my suggestion, its a quick easy test. Good luck!

 

[WyoSyclone]

Re: Tracking big resistance in wires, plz help

I do, two of them, and trust me they have been thoroughly investigated.

Where are the gains set on these amplifiers..... 99% of the time that's the problem with alternator whine....

Do this....
1. turn the gains on the amps all the way down, then open them just a small fraction.
2. turn the radio on and turn the volume up till you get distortion - the system shouldn't be that loud since the amp gains are turned all the way down... if so, turn the amp gains down more.
3. turn the radio volume down until the distortion JUST disappears, then leave it there.
4. turn the amp gains up to your desired maximum loudness level.

Doing this procedure optimizes the signal-to-noise ratio between the radio and amplifiers and keeps the noise floor (alternator whine) low.

Post back on how high your amp gains were turned.....

 

[BoostedSUV]

Re: Tracking big resistance in wires, plz help

^listen to Rob, he knows a thing or two about car audio.

I have never gotten an engine whine from gain levels being turned up too much but I did get a lot of "white noise" from the amps trying to amplify a low level signal from the radio. I learned that turning gains all the way down, turning radio to about 80percent of its volume range, then slowly turning gains up until you get your max volume level (just before distortion). Like Rob said, that's the best way to get matching level signals from the radio to the amp.