Alternating current in charging system

Hello all:

I'm stumped. I installed an aftermarket car stereo in the '60 and it lasted about three months,  then it started acting so strangely I had to get rid of it, and bought a second one. This one works fine with the key in accessory position, but when the engine is running the audio is either non existent or cuts in and out so much it's not useable. Long story short, I checked the voltage coming in on the Ignition wire, and there's actually more alternating current than direct current! (about 18V AC and 12.5V DC) That can't be right- it has the original generator and electromechanical voltage regulator. The TSM doesn't say anything about rectifying the current coming from the generator, which makes sense as it isn't supposed to be putting out any AC at all. I have a feeling any aftermarket anything I put in here is going to go bad- I don't have much experience with this kind of system; does anyone think I should be looking at the generator itself? The TSM does mention "polarizing" the generator, but if the windings are going the same way there shouldn't be anything "alternating". I tried putting diodes in line with the power leads to add rectification but it didn't help.  I added a noise suppression condenser on the coil and that didn't do anything either. (I assume the Ignition wire feeds the coil and shouldn't be getting anything backwards from it.) Any input appreciated.

CN


Edited by cnagorka - Oct/31/2014 at 1:26pm

Ok first what are we working on year/model/motor wise?
Dose it run a generator or alternator?
Why are you checking “the voltage coming in on the Ignition wire” and where is this wire located at?
What wires did you reverse to change the readings? Change them back the way they were. Or was this your meter leads?

I am no expert but my take on how I would do this.
Find a fuse in the fuse panel that gets volts with the key in run & ACC position. Check this fuse with meter-red to the fuse and black to anybody ground and why do you get? Should read 12 volts +/- a volt.
This is where I would pick up power at for the radio. Ground should go to and good clean body ground.
Speaker wires both + and – (2 to each speaker) should run from radio to the speakers. Do not run the speaker – to body ground.
Dave ----

I would not use that wire that feeds the coil. Does your car not have a fuse panel? I have seen posted that older car did not have a fuse panel.

Now for testing only what if you ran wires from radio to the batt. does it work as it should or still have issues?
If works then I would wire the radio up using a relay and triggered from your IGN. switch but not from the wire feeding the coil.
Dave ----

They used to use something called a growler to check the generator armatures that there were no open spots to the commutator. Commutators regularly got dressed on a lathe. Other than that if the brushes, bushings and field windings are good the generator should be OK. I don't know if anyone still tests them for output or whatever. Old cars certainly had generators and radios working together without problems. Some of them nay have been tube radios.