New member to the site but have used the threads a lot to trouble shoot.

Here's my problem.
I have a 1970 Pro Street Cuda that I have changed to electronic ignition and then to a MSD system.
Last weekend I was coming home from a car show and noticed the car wasn't charging. I checked the alternator and found the brush to the field (green wire) had come out. I ordered a rebuild kit and replaced it.
When I started the car the volts jumped up to 16 at idle and higher with RPMs.
I thought I fried the regulator. So I changed it. No change. So I replaced the alternator. No change. So I looked at some other threads on this problem and did some trouble shooting.
Removed both wires (green and blue) from the alternator and started. No charge. That's good.
Hooked up only the blue wire and had sparks and high charging. That's bad!
Hooked up only the green wire and no charge. That's good!
Removed the wires from the regulator with both green and blue wires connected and had charge. That's bad!
Yes, I checked grounds all were good.

Any clue?
Thanks,
Chaotic Cuda

 

Here's how these work, and thank your lucky starts you didn't do "this" to the other field wire

The blue field wire is switched 12V ignition (assuming factory wiring.) IT IS NOT FUSED This supplies 12V to and through the field, which is nothing more than a Great Big electromagnet

The VR regulates voltage in the case of the 70 / later stuff by "controlling the ground" to the field circuit via the green wire

WHAT YOU DID:

Either you broke, or left out, or got the wrong brush, and when you put it back together you GROUNDED that brush. This essentially causes the thing to charge "full output"

When you get it out, fixed, take your meter and check continuity between the two brushes. You should show a very low reading. Rotate the pulley. It will go up and down somewhat

Check each brush to the alternator case. Should show "infinity" that is, no continuity.

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If you would have been so unlucky as to have done this to the "blue" field wire, this would have shorted 12V right to ground, and you'd either have a melted harness, or "maybe" a blown fusable link

ALWAYS check these, and especially on rebuilt ones if you buy one

 

440 RoadRunner Thanks!
I took both the original and the new alternator to Autozone today and had them tested. Both came up good.
Bought another regulator and installed it all. And guess what it still is over charging.
So tonight I'll remove the alternator and test it as you suggest.
I'll let you know what I find out.

Also will this fry the regulator?

Thanks,
Chaotic Cuda

 

Well, I found the problem. After pulling the alternator I went back threw everything and found the screw on the brush was grounding out.
Replaced the screw and the isolated washer and all is charging like it should.

Thanks for the help.

 

Exactly what I told you, LOL. No it won't hurt the VR

Tuck this away for the future:

Remember, the 69/ earlier had one grounded brush. You REALLY have to "watch" rebuilts. Under no circumstances allow them to sell you the older "roundback" style, and REALLY under no circumstances allow them to sell you a 69 type that has been "backyard converted" to isolated field by the Mexi-nese rebuilder

This is a 69 / earlier original alternator which has been "hacked" by a rebuilder to accept an isolated brush, so they can sell them as a 70 / later. Do not accept one. This one still has the grounded 69 type brush the phillips screw at the bottom at 6 o'clock, and the original isolated brush at 9 o'clock

The hole at the top, 12 o'clock is where the 'hack' was



On the right is a mid 70's "squareback" and what you should accept regardless of year. These are a better design, and can be used on the older 69 / earlier my merely grounding one brush.

On the left we have an interesting 'deal.' This evidently has an aftermarket casting, or was limited production. I've never seen one. This one has the 69 / earlier grounded brush at 9 o'clock, an isolated brush at 12 o'clock, and AND OPEN place for an isolated brush at 3 o'clock. This is not a hack. It was made that way