ok, i have a 69 chevelle (350)with an aftermarket cd player in it. it worked fine for a long time. recently i have been having a lot of problems with the electrical system, and im kind of stuck here. the problem is not that the radio does not turn on, but that when on, it will only utilize the speakers if the engine is at idle, but as soon as i rev it up the speakers kind of pop and nothing till it gets back to idle, then they pop back in.

before all this started happening, when the radio was fully functioning, there seemed to be a strange whistling type noise(hard to explain) coming from the engine, that somehow seemed to be in conjunction with the dashlights dimming and lighting ultra bright at random.

after putting in a new alternator, a new battery, a new voltage regulator and still having problems keeping precious power in the battery to start the car had taken my car to get the electrical system checked couple of weeks ago and they said my alternator (brand new just bought)was not putting out enough juice, so i traded it for a new one at autozone.

so now, the battery doesnt die anymore, but the radio is going nuts.

if anyone can help i would appreciate it, and if you have questions ill try to answer to the best of my ability

A stab in the dark, but worth checking -- is the radio ground wire connected to the dash lights. I've seen it more than once where the radio installer will probe the wiring harness with a test light looking for a ground wire. He'll find a "ground" but it will turn out to be the dash light dimmer circuit. Ensure that your radio ground wire is connected to good chassis ground.

I'd have someone check out the changing system. The voltage out of the alternator may be going out of regulation causing the radio to shut down. Sounds like the radio may be trying to protect itself and the lights are going bright/dim because of it.

I would run 2 temp wires right from the battery (1 neg and 1 pos), This will ensure a good 12 volt source and a good ground. Connect them to the stereo and see what happens. Hope that your weird power issues didn't break something in your cd player.

I'd have someone check out the changing system.
I agree with John, you have charging system or wiring issues. For a simple test you can do yourself, check the voltage at the battery with the car running at a fast idle, should be 14-14.5 volts. If you are getting 15+ the radio with shut off to prorect itself.

This was happening with my sons 66 Nova. We had the wrong fuse in the fuse box for the radio. It was letting too much voltage to the radio and it would shutdown, changed to the correct fuse and no problems since.

This was happening with my sons 66 Nova. We had the wrong fuse in the fuse box for the radio. It was letting too much voltage to the radio and it would shutdown, changed to the correct fuse and no problems since.

Just for the record
That can't be the reason, a fuse either lets full available voltage to pass through or blows and stops all voltage if the current is too high.
The fuse size has nothing to do with limiting voltage.
You just thought that was the problem.

ok update.

im thinking that it is a charging problem, as today, my home cooked heater switch (hooked a wire from the bat to the fan with a switch placed under the steering wheel) has blown its fuse after several months. put a new fuse and popped right away.

now the radio, it now seems the problem is intermittant, as when driving home from work, at first the problem is there, but after warming the car up, the radio was working fine.

i will try out some of these suggestions tomorrow as i have school tonight.

thanks for the replies

battery when car not started is 12 or so volts
with car running at fast idle it is over 18

im thinking i will put another voltage regulator in it, as the alternator is brand new, but if it doesnt solve the problem, i may get another alt.

maybe ill take it to autozone to see if they can check my alt. is there a way for me to do it here with the voltmeter? maybe if i knew what the three wires were on the back of it

back to work

battery when car not started is 12 or so volts
with car running at fast idle it is over 18

That is definitely your problem. It may be the regulator or wiring issues. If you are going to replace the alternator, convert to a internally regulated alternator, very easy to do. post back if you have questions. To troubleshoot the externally regulated system see below.......
This was written by another member, a very good write up on how it works and how to troubleshoot a externally regulated charging system.

I dug this out from before, hopefully it help. If not, just post or send me your questions.

I'll try to provide a simplified explanation of how the externally regulated alternator and regulator work here. This explanation starts from a parked car with engine off state.

The regulator brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white regulator #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the points.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the points I kept mentioning. Then the voltage drops and the points close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F or #1 terminal (field) - KOEO = #4 slight voltage, KOER = 9-12V typically
#2 terminal (sense) - KOEO = 0V, KOER = >3.2V
#3 terminal (Battery) - KOEO = 12V, KOER = 12V
#4 terminal (light) - KOEO = F slight voltage, KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but could be up to 14.5V when engine is running.

Check the light: Ground the brown #4 terminal wire at the regulator. When grounded the light should come on. If you don't have a light then skip this test. Test this with the connector off the regulator.

Checking the alternator: Jumper the blue wire F terminal to the battery post on the back. This should make it easily crank out 16+ volts. Next, connect a troublelight between the battery post and the F terminal. The light should come on and you should measure > 3.2V at the other alternator terminal. If it passes these tests, then it's in the regulator or wiring.

Checking the wiring: At the regulator connector jumper the brown light wire (#4) to the F terminal (#1) and you should be able to measure >3.2 volts on the other alternator terminal or terminal #2 of the regulator connector. If these tests pass, it is in your regulator.

When doing these tests, make sure you turn off or pull the fuses for any added electronics that you can. The alternator test can produce enough voltage to damage stuff.

Peter