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Discussion Starter #1 (Edited)
My stereo in my 70 Camaro is getting power from the BAT and ACC terminals on my fuse panel. The wires connected to these Terminals are showing the correct 12 volt DC. However, I am also getting an AC current reading on these wires. This causes the car stereo to shut down and not turn on. What could cause this? EI Distributor?

Rather than tracking down the problem is there some sort of filter that removes the AC current that I can splice into the wires going from the fuse panel to the stereo ?

Here are pictures showing where the 2 stereo wires are attached to the BAT and ACC in the fuse panel. There is also something connected to the IGNITION terminal. By the way what is the big silver canister on the fuse panel?

 

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The silver cannister is the emergency lights flasher.
BAT is for clock, station memory and presets memory.
IGN is for power turn on.
Brown wire with round terminal, I bet, is for parking brake switch, BRAKE light comes on with parking brake set to on, off when parking brake released. Switch maybe broken since its not hooked up or cables need lubing.
 

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One of your diodes in your alternator is probably failed or failing. Thats about the only place to get an AC component into the cars electrical system.

Does the battery drain over time?
 

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Discussion Starter #5
One of your diodes in your alternator is probably failed or failing. Thats about the only place to get an AC component into the cars electrical system.

Does the battery drain over time?
The battery has not drained in the month I have had the vehicle. Drive it everyday. Alternator is new.
 

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Discussion Starter #6
The silver cannister is the emergency lights flasher.
BAT is for clock, station memory and presets memory.
IGN is for power turn on.
Brown wire with round terminal, I bet, is for parking brake switch, BRAKE light comes on with parking brake set to on, off when parking brake released. Switch maybe broken since its not hooked up or cables need lubing.
Thanks, would any of this cause AC leakage into the BAT and ACC terminals?
 

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My stereo in my 70 Camaro is getting power from the BAT and ACC terminals on my fuse panel. The wires connected to these Terminals are showing the correct 12 volt DC. However, I am also getting an AC current reading on these wires. This causes the car stereo to shut down and not turn on. What could cause this? EI Distributor?

Rather than tracking down the problem is there some sort of filter that removes the AC current that I can splice into the wires going from the fuse panel to the stereo ?
When you are being shown this correct 12 volt DC, is this with the engine off but the key in the run or accessory position ?.

What AC current reading are you getting and on what wires ?.

Is the stereo new, used, old, or of unknown quality ?.

Is the stereo connected directly to speakers or is there an amp involved ?.

I'm not a fan of putting on filters but I wonder if there is a problem with the stereo getting too much voltage when the engine is running ?.

I wonder too is it's an older stereo that maybe some filter caps have dried out or vented allowing noise into the system ?.

If the radio is connected directly to speakers, are one or more possibly shorted to the chassis of the car to where this could be causing the radio to have noise ?

If an amp is involved, are the gains properly set, RCA's run properly or is the amp of questionable quality ?.

I've troubleshot alternator whine in car audio systems through the years and I've always seen some AC ripple in the DC lines. Your alternator produces AC but then the diode tree converts it to DC but these diodes are not an absolute. Some AC still gets through.

Jim
 

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Discussion Starter #8
I just checked again and with the car off the BAT terminal on the fuse panel is giving 12.3 volts DC and 26.5 volts AC. This has to be the problem. How the hell can AC current be showing up on my multi meter when on a DC circuit from the battery.

When you are being shown this correct 12 volt DC, is this with the engine off but the key in the run or accessory position ?.
-BAT terminal on fuse panel reads 12.2 volts when engine is off. ACC reads 12.2 when key in ACC position, 14.0 - 14.1 when running. Radio does not turn on in ACC position but sometimes I can get it to turn on if I turn the ACC position on and off about 5 times.

What AC current reading are you getting and on what wires ?.
- I get between 20 and 25 volts AC on the BAT and ACC wires.

Is the stereo new, used, old, or of unknown quality ?.
- Brand new, second one I have tried of the same model radio. Radio is good.

Is the stereo connected directly to speakers or is there an amp involved ?.
- No external amp, biult in 50 x 4 (200 watt)

I'm not a fan of putting on filters but I wonder if there is a problem with the stereo getting too much voltage when the engine is running ?.
-Voltage with running engine is never higher than 14 - 14.1 volts. DC voltage is not a problem, numbers are all in the correct range.

I wonder too is it's an older stereo that maybe some filter caps have dried out or vented allowing noise into the system ?.

If the radio is connected directly to speakers, are one or more possibly shorted to the chassis of the car to where this could be causing the radio to have noise ?
-Professionaly installed speakers and wires with proper insulation.

If an amp is involved, are the gains properly set, RCA's run properly or is the amp of questionable quality ?.
- No amp

I found this 15 amp noise filter, since my radio requires a 12 volt from the BAT and a 12 volt from the ACC would I need 2 of these?
http://www.crutchfield.com/p_003S15A/American-International-S-15A-S-25A-15-amp-250-watt.html?tp=2653&tab=detailed_info
 

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Try another voltmeter. The only way you will get AC voltage that high is if the rectifier bridge in the alternator is cooked.
 

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Try another voltmeter. The only way you will get AC voltage that high is if the rectifier bridge in the alternator is cooked.
X2 on another meter. With the engine off, just battery power, meter should indicate 0 VAC if meter is of better quality.
 

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One of your diodes in your alternator is probably failed or failing. Thats about the only place to get an AC component into the cars electrical system.

Does the battery drain over time?
X2 on alternator diodes.

You can install filters, but those only remove noise signals that are in the millivolt range. What is the magnatude of your AC voltage reading? If it's enough to cause your radio to shut down then I'm with Mark - the alternator has a bad diode.
 

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How to fix the volt meter
Turn it over, reas the fine print down the bottom
If it says "made in china"
Turn the voltmeter back over...get a scewdriver and stab it very hard many times.

Never buy or use one of the cheaper multi meters...get a tradesman quality....by the time you go thru a string of cheap ones you could have brought a tradesman unit

I never followed the advice....Been there done that..

The other thing you could be reading is a 1/2 sign wave which is basically a DC current not alternating from pole to pole.

Even thu the battery is not going flat, the diodes or bridge can be faulty....your battery will get low if you do a lot of cold fire up and short distance running or night running.
The batt will still show voltage in correct range but have low storage.
 
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